[disneyd]

I've got a varmit AR with a 20" bull barrel, 1:8 twist.

I've tried factory 55 grain loads as well as my own using carefully prepped cases and Hornady 55gn FMJ BT bullets. No matter what, I get a fairly big group at 100 yards. Usually around 3". Velocity is right at 3100 fps on my reloads varying by about 10 fps.

I also have a load I recently developed using the same powder (AA2230), cases, and primers that I used with the 55gn bullets, but am using a 60 grain Hornday VMax bullet. These run right at 3000 fps with about a 10 fps variance. With this load I am getting consistent 0.5" groups... no kidding, most of the time the holes overlap and it turns into one slightly larger, ragged hole.

I've shot both these loads on the same day within minutes of each other with the same results. Any idea why there is such a big difference in accuracy? Is the 1:8 twist just too fast for the 55gn bullets? I wouldn't have though going up 5 gn to 60 would have made such a difference.

[ocabj]

The Hornady 55gr FMJBT is a bulk bullet not designed for accuracy. Also, since you're shooting at 100 yards, a BT doesn't help much. Believe it or not, flat base bullets are better for short range because they stabilize faster (and also lose stability faster).

The Hornady V-Max is a better design than the 55gr FMJBT.

1:8 is not too fast for the 55gr. The bullet is simply just not very good for accuracy. USGI M193 which uses a 55gr bullet performs about the same as what you're experiencing with your handloaded 55gr rounds; 3MOA.

If you want a nice short range bullet, try the 52gr HPBT design like the Sierra Match King or Nosler Custom Competition. Check the Nosler website and you'll see you can get 1000 52gr HPBT 22cal bullets for a good price with low shipping costs direct from Nosler. A 69gr HPBT is also a good bullet for 100-200 yards.

[taliv]

hard to say; .5" to 3" is definitely unusual. if you'd said .5" to 1.5" i would have chalked it up to cheaper bullet construction.

on the 3" groups, are they round? strung horizontally or vertically? how many rounds per group are we talking here?

[gyp_c2]

Have you tried lowering the velocity to 3K on the 55gr slugs?
Maybe worth a try and save some pennies too...;)

[disneyd]

Thanks for the advice so far guys. Ocabj, I'll give those 52gn HPBTs a try.

Taliv, here are a couple of targets:

This is typical of my 55gn loads. The POI is high because I'm zeroed for the 60gn loads. I guess this one is actually more like a 2" group if you don't count the one that hit low and to the left... I'm gonna blame that on the muzzleloader going off at the station next to me (flinched a bit). What does the circular pattern mean vs horizontal or vertical stringing?

http://rx7.voodoobox.net/images/55gn.jpg

Here is one of the 60gn targets. Five shots in there. The weird mark at 10 o'clock is shrapnel from something on the range. I think someone else at the range hit one of the 2x4 target stands up-range.

http://rx7.voodoobox.net/images/60gn.jpg

[GlockTerrier]

The POI is high because I'm zeroed for the 60gn loads...


Just an observation : from the purely external ballistic point of view the difference in POI between 55gr@3100 and 60gr@3000 @100yards is negligible - definitely less than you're seeing...

I think it is hard to explain this... Maybe the deformation wave in your barrel (those barrel "harmonics") disperse the bullet trajectories for this load. Since a bullet weight difference is relatively small - it'd be interesting to see what effect on accuracy a lowering of the speed of your 55gr. to 3000 - the same as your 60gr - would have...

[asknight]

I think GlockTerrier is getting to the point. Either slow down or speed up the 55gr to get it out of the barrel at a different "time from ignition" as your barrel harmonics are causing the bullet to leave the barrel during max deviation of "whip" cycle.

Of course, this is *usually* very noticeable during load work-up in certain preset increments of powder charge. Your groups will shrink and expand during power charge increases, until max is reached.

This is also a theory I attribute to the guys who say they had to load a touch over book listed max to get best accuracy. In other words, they likely could have backed off a touch from max and obtained peak accuracy as well!

Looks like your 60gr load is a keeper, though!

[disneyd]

Of course, this is *usually* very noticeable during load work-up in certain preset increments of powder charge. Your groups will shrink and expand during power charge increases, until max is reached.

I'll try loading some down to 3000 fps. However, as you mention above, when I was developing the load I went from 2800 up to the current 3100 fps load and didn't see much difference in accuracy in any of the loads. I stopped at 3100 because the primers started to flatten slightly above that and i wanted a load that was a good all around load that wouldn't be hard on the brass or rifle at all.

How about OAL? The 60gn were 2.250 and the 55 were 2.225. Would .025 make that much difference?

I'm also going to pick up a few vmax or similar quality 55gn bullets and see if they make any difference.

[Walkalong]

ocabj got it right, right off the bat.

Cheap bulk 55 Gr. FMJ vs and excellent bullet - the V-Max

Tweak it, but if you get the 55 Gr. FMJ under 2" I'll be suprised. Been suprised before though. :uhoh:

[GlockTerrier]

...when I was developing the load I went from 2800 up to the current 3100 fps load and didn't see much difference in accuracy in any of the loads.


I think this is an important data point that may eliminate dynamic barrel "whip" factor from the equation. Which pretty much leaves us with the simplest and already mentioned several times theory that the difference in the bullet flight explains it all. Come to think of it - slightest bullet shape/weight disribution imperfectons/changes can significantly affect bullet flight through the air.

FWIW I've observed signifcant (2-3") and persistent 100yard POI shifts just going from 69gr SMK to 68gr Hornady at the same speeds that cannot be explained by differences in the externall ballistic trajectories. Actually - any bullet change I've tried resulted in significant POI shifts at 100 yards.

If the bullet flight is so different that moves POI several inches around - it probably should be no surprise then it as easily affects accuracy of different bullets as well - depending on consistency of factors involved into defining bullet aerodynamics...

[DWARREN123]

No mystery, it's what the barrel likes. Each barrel is a law unto itself.

[GlockTerrier]

No mystery, it's what the barrel likes. Each barrel is a law unto itself.

If anybody has a barrel that shoots these bulk 55gr as good as disneyd's shoots his 60gr V-Max'es please let everybody know - I for one may be interested to get the same...

[taliv]

i have two rifles that shoot pretty decent groups with super-crappy ammo (M193 pull-downs, resized, but still with fairly deep pull marks). they'll do a heckuva lot better than 3 MOA for sure. 1.5 MOA I'd say. barrels are white oak, and rock creek. They do the same with bulk Rem 55g, but I haven't tried the bulk Hornady. Groups get a whole lot smaller when I switch to sierra 69g, but still not 1-hole, as neither of these rifles is scoped and I can't see the target that well.

I don't think that problem is entirely the cheap bullets.

[Art Eatman]

Maybe 1:8 twist is a bit fast for the 55-grain bullets?

My 77Mk II has a 1:12 twist, and I get 1/2 MOA with 55-grain bullets.

Art

[BAT1]

I'm thinking twist rate might be a factor too. My Bushy carbine is 1:9 and it is accurate with 55 gr ammo and better with 69 gr reloads. try a larger bullet.

[Walkalong]

I get 1/2 MOA with 55-grain bullets.
Cheap bulk 55 Gr FMJ or good 55 Gr bullets?

[rcmodel]

Bulk 55 grain FMJ-BT bullets from Hornady & Winchester won't group worth sour apples in any rifle I have tried them in. But they make great cheap blasting ammo.

If you want accuracy, V-Max & Nosler Ballistic-Tip's are often hard to beat, even with match grade 52 grain HP's.

This from a Colt SP1 Sporter 1/12 with Nosler BT's & FMJ-BT 55 grain bullets..
http://i81.photobucket.com/albums/j219/rcmodel/KTOG/EoTecGroup.jpg

My CZ-527 shoots 55 grain FMJ-BT just about the same as this.
It's a one-holer with 55 grain Nosler BT's.

http://i81.photobucket.com/albums/j219/rcmodel/KTOG/1224.gif
rcmodel

[GlockTerrier]

This from a Colt SP1 Sporter 1/12 with Nosler BT's & FMJ-BT 55 grain bullets..


Thanks, rcmodel! I'm curuios did you ajust your zero between these two groups? I find this change of POI intriguing....

Maybe it is just coincidence - but when I switch to bullets with lower aerodynamic quality and consistency (like 55gr TBBC SP - not cheap by any means barrier penetrator, but head-heavy with with poor aerodynamic and I can't get any consistency with them either) I often see this sudden drop to right and down measured in inches without touching elevation or windage adjustment on a perfect calm day... As if they just do not fly as "true" as the match bullet.... Switching to a better bullet (better BC and consistency) shifts a POI usually up and to the left for me.... POI shifts due to bullet change (approximately with the similar speed/weght) can be as large as 1-2 moa at 100yards..

Here's one homegrown hairbrain theory of mine if anybody cares: :)

If there are boaters around here they should be familiar with a phenomenon of a "prop walk" - lateral force arising due to "screw-like" rotation of the propeller in the water. Depending on direction of rotation you experience "walk to the port" or "walk to the starboard".

If there is some yaw in the flight of fast spining bullet it behaves in the air similar to a prop in a water and a bullet "walks". Amount of yaw and its effect depends on on the bullet shape, mass distribution, velocity and is individual to to a particular bullet/velocity combination.

Gun can also come into equation but as a secondary factor here with its ability to effect concentricity of the bulet during firing (jump to the lands, point/surface damage/deformation during chambering, firing etc.) Then the accuracy is a function of consistency in a yaw characteristics. I've noticed a significant shifts in 100yards POI even between two match grade but different bullets w/o effecting the size of the group. So amount of "walk" and its consistency (ability to maintain the same walk) seems to be different for different bullets.

Now it is also known that it takes time to "stabilize" the bullet (especially heavier and longer long-range ones) - that means that in time an amount of "wobble" in the flight decreases diminishing the "walk" making long-range shooting possible. Our "sighting" or "zeroing" procedures automatically adjust for the specific bullet "walk" at the specific distance - but a change of the bullet would have us to readjust the "zero" again.

Main point here is that unexplainable otherwise shifts in POI and an accuracy of different bullets under similar other circumstances may be related and have the same root cause: "bullet walk" and its consistency.

Absolutely concentric bullets with uniform mass distribution and ideal center of mass position for its shape should be in (this) theory the most accurate bullet - in any gun.

[redneck2]

There was an article in Handloader some time back about accuracy 30-40 years ago versus today. A true 1" rifle was almost unheard of in the 60's, but is nothing special today.

Taking old ammo and shooting in new rifles gave larger groups. Taking today's ammo (bullets) in old rifles gave sub 1" groups.

I get WAY under 1" with my 1-9 Bushie Varminter with 50 grain Noslers.

[rcmodel]

Thanks, rcmodel! I'm curuios did you ajust your zero between these two groups? I find this change of POI intriguing....Yes, I beleive I did.

I was sighting in a new EoTech I had just put on the AR that day. I think I made the final adjustment change after shooting the FMJ-BT group.

Changed ammo to the Nosler reloads at the same time because that was what I wanted to be zeroed with when I got done.

http://i81.photobucket.com/albums/j219/rcmodel/KTOG/1224.gif
rcmodel

[GlockTerrier]

Thanks, rcmodel! I'm curuios did you ajust your zero between these two groups? I find this change of POI intriguing....

Yes, I beleive I did.

Here "walks" very nice theory... :) I do have similar targets - but w/o adjusting sights, though - just by changing to ammo with a different bullet.... :) Am I alone who sees bullet-induced POI shifts?

Although Redneck2 also provided very interesting data points to support the assertion that quality of bullets have relatively more effect on accuracy than the gun they are fired from.

This, of course is obvious - the moment the bullet is out of muzzle with its vector of speed and speed of rotation parameters set - the gun fulfilled its role and has nothing more to do with where this bullet lands. It's all between bullet, air and a gravity from that point on according to the common laws of physics....

[rcmodel]

Am I alone who sees bullet-induced POI shifts?Of course not!
I would be more surprised if I didn't have a pretty large POI shift when changing ammo brands or bullet weights.
A very few rifles are pretty consistant, but the large majority are not.

http://i81.photobucket.com/albums/j219/rcmodel/KTOG/1224.gif
rcmodel

[GlockTerrier]

I would be more surprised if I didn't have a pretty large POI shift when changing ammo brands or bullet weights.

Just to be clear - I meant "abnormal" POI shifts that are well beyond theoretical ballistic trajectories - which can be seen at short distances like 100yards.

At flat 100yards shooting (unlike say, 300-600 yards) theoretical (ideal) trajectories in most usable weights, speed ranges and ballistic coefficients wouldn't differ more than 0.2" for .223.

Instead, after zeroing with a match bullet at 100 yards into X-circle, switching ammo to lower quality generic bullets I often can see relatively larger group with center dipping lower and to the right as far as 2". Now if I zero for this bullet, then the return back to a match bullet this will appear as noticeable POI shift higher and to the left.

Anybody noticed something like that? :) Or is this just my imagination and false conjecture due to limited number of observations and coincidences?

If this would be a confirmed observation there may be very interesting practical implcations for load development , I think.... But I don't want to run ahead with this until we can establish that such thing as flat line close range (100yard) significant bullet-induced POI shift indeed exist :)

[stubbicatt]

Glock Terrier said: If anybody has a barrel that shoots these bulk 55gr as good as disneyd's shoots his 60gr V-Max'es please let everybody know - I for one may be interested to get the same...

I've seen my girlfriend put 10 rounds into about an inch at 100 using Hornady 55 grain FMJ bullets, mixed military cases, CCI 556 primers, and 25 grains of Ramshot TAC. This from prone with a bipod, a 4x scope, and a Vector V93 rifle. I actually saw her do it twice the same day.

Now me on the other hand, I wish I were as good of a shot as is she.

[rcmodel]

I think.... But I don't want to run ahead with this until we can establish that such thing as flat line close range (100yard) significant bullet-induced POI shift indeed existAgain, yes, it exists.
Depending on the rifle, it can be inches at 100 yards.
I've seen it happen for 45 years or so.

BTW: New Shooting Times has a test report on the Remington Power-Level .300 RUM loads. They reported a shift 5.25" high & right when switching from full power to .300 Win power level.

When switching from full power to 30-06 power level, POI changed to 1" low & 3" right.

Individual power levels grouped 1.82", 1.24", & 1.70" when shot separately.
Overall combined group size of all three loads was 6.0" at 200 yards.

Is this evidence enough?

http://i81.photobucket.com/albums/j219/rcmodel/KTOG/1224.gif
rcmodel

[GlockTerrier]

rcmodel: Is this evidence enough?
Maybe :) Thanks, rcmodel - I don't doubt your word - just wanted to be clear about the kind of POI shift I had in mind and keep some healthy scientific scepticism about the value of limited sampling in personal observations.... :)

Let's assume that the short line bullet-dependent POI shift objectively exists and the precession/yaw/wobble-induced "bullet walk" is indeed responsible for it. What follows is another hairbrain speculation of mine - so bear with me, if you can, here... :)

This may have an interesting application for a quick selection of best perspective round for the rifle and estimation of a bullet quality - as they leave the barrel of your rifle for an autonomous ballistic flight (keeping in mind that a specific gun during firing process "imprints" itself on the bullet affecting to various degree its aerodynamic qualities)

During load development the attention is usually on the size of the group - and this is a measure of consistency in the walk. But if the "bullet walk" theory is even approximately correct the POI position itself is also an important observation that tells us about amount of walk - or an amount of precession/yaw/wobble of the spinning bullet in flight.

If all the rifles have their rifling twist in the same direction - the bullet always walks in the same direction - let's say - to the right. Up or down I'd think is less important and is probably related to the shape and mass distribution that changes amount of cumulative positive or negative overall aerodynamic "lift" the bullet gets during a revolution due to assymetrically rotating yaw/precession angles periodically changing its "angle of attack". (if Rcmodel also makes planes he will understand me :) )

So - if I shoot several groups with different loads/bullets without changing the rifle zero - the one with a group average POI to be farthest to the left has a minimum amount of walk (or precession/yaw/wobble induced lateral travel to the right) and should be closest to ideal "truest" bullet! Again - we're talking about the aerodynamic quality of bullet as it is "imprinted" with your gun during firing - and not its "original" out-of-the-box condition. And this is exactly what we're looking for!

Now, I'm not saying that that the "leftest" group will be most accurate - although it very well may be. The walk on average can be small - but still not consistent enough. This may very well be related to gun "imprinting" now rather than to the bullet that already proved that "on average" it flies "truest". What we have here is potentially the best candidate among tested - so we may start working on fine tuning "imprinting" factors for it- speed, jump to the lands, barrel rifling qualities (this would explain the effect of some "firelapping" techniques on accuracy), ramping and chambering mechanics etc. Of course, lack of constency still can be caused by the bullet physical inconsistency due to manufacturing tolerances - then very little we can do and we can go on to fine tuning the next most accurate group on the left as the next best candidate.

Overall, if this works - tracking short-line (~100y) average POI position may be an easy additional guide to significantly accelerated accurate load development. Of course, if one already shoots one hole like disneyd does with his 60gr V-Max load - one can stop right there... :)

I'd be interested to hear personal obeservations or published results that may add credence or disprove this speculation about "leftest group to have most accuracy potential". (assuming that all rifling twists in the same direction - I have no idea if this is true, actually... If yours twists in the reverse direction -it would reverse the rule to the "rightest" group)

Thanks!

[crux]

Anybody got a world class air rifle or pistol? It would be interesting to see POI impact shifts of pellets of the same weight, and different designs. Just brain farting..........

[GlockTerrier]

crux: Anybody got a world class air rifle or pistol? It would be interesting to see POI impact shifts of pellets of the same weight, and different designs.

Thanks, crux! Very clever suggestion! (too bad I don't have such rifle :) )
The only thing is that I have no clue on dependency of the size of assumed effect relative to speed/size...

The supersonic flight, very fast rotation and longer distances for shooting may create an effect easily measurable in inches. On the other hand slower subsonic flight, slower rotation and shorter distances may create a much smaller effect in POI that can be easily lost in the noise of random shifts of POA (point of aim)...

The slow subsonic "bullet" may have to be larger (like baseball or golf or tennis ball) to create "curved ball" effect due to rotation. (which balls of course "curve" for a different reason - friction of the surface) But who knows.. - anyway, the suggestion is certainly would be interesting to check on - Thanks!

[rcmodel]

First, you have to accept that "bullet walk" is whats causing it.
I don't!

Change in POI is caused by differences in barrel harmonics with different bullet weights, bearing surfaces, etc.
Simple as that.

Bullet walk is always present at long range, but it is always consistent with an accurate load.

I have watched too many .30 caliber bullets through a spotting scope doing the corkscrew on the way to the 1,000 yard targets to believe "bullet walk" has any effect on accuracy.
They walk all over the place for quite a ways, but they still all hit pretty much in the same group.

http://i81.photobucket.com/albums/j219/rcmodel/KTOG/1224.gif
rcmodel

[peterotte]

Here's one homegrown hairbrain theory of mine if anybody cares:

You got that one bang on GlockTerrier. A good analogy. The bullet spin and yaw causes a spiraling flight path that can dampen down or get worse. I wonder whether the muzzle crown could influence boat tail yaw. I suspect that the small chamfer one often finds on a crown could be making matters worse. There is a web-site that describes the phenomena.

Check this one out!

http://www.nennstiel-ruprecht.de/bullfly/index.htm#Figures

[GlockTerrier]

Change in POI is caused by differences in barrel harmonics with different bullet weights, bearing surfaces, etc.

Well, the "barrel whip" theory as the answer to all ballistic questions as pertinent to reloading doesn't satisify me - YMMV, of course. (In fact I tend think it was overhyped for reloading masses and may be almost totaly irrelevant for load development and is primarily of interest for the rifle designer...) It certainly doesn't offer any convincing insights to the question posed by Disneyd and significant lateral POI shifts I've observed after the switch to different bullets.

1. Reloading public somehow decided that they can "time" the bullet speed in the barrel "to catch the barell muzzle" at the point of minimum amplitude. Maybe they are not aware that the physics of the barrel whip *always* makes the muzzle an "anti-node" in deformation waves - the point of maximum whip amplitude and speeds.

2. The physics of rifle barrel whip concentrates its energy mostly in the vertical plane - leaving significant *lateral* POI shifts for different load/bullets completely unexplainable.

3. The parameters of the whip are defined by almost constant resonant parameters of materials, construction and masses involved and should be very stable. To expect to change them just by changing the load within normal working ranges is as likely as to expect change the tone of the guitar string from E to C just by playing a bit softer... I'm sure that Disneyd's barrel "whips" absolutely the same for all it counts with 55gr@3100 as it does with 60gr@3000...

4. If the barrel whip was a major factor in accuracy we'd have heavy short pistol-length barrels with rifle scopes blasting the heck out of long varmint rifles in accuracy.

5. Redneck2: Taking today's ammo (bullets) in old rifles gave sub 1" groups. I wonder if barrel whip theory was used in 60s to explain their group size - what would they say then if they knew what we know in 21st century?

In general I find the whole preoccupation with rifle-related factors in working on accuracy of a modern firearam ammo a bit obsessive.

Yes, some guns are constructed in general more accurate to aim and shoot than others, barrel whip, floating tubes and all. But ultimately it's not the gun that punches the holes hundreds yards downrange - but the bullet, - and it has yet to get there on its own and a lot can happen on the way in the supersonic flight through dense supercompressed air. Funny thing is that we know what even a light breeze of air can do to POI at mid range distances but are still peering into the gun in search of answers to subMOA accuracies...

[GlockTerrier]

peterotte: Check this one out!

http://www.nennstiel-ruprecht.de/bul...ex.htm#Figures

Wow! Thanks, Peterotte!
As always all the good thoughts were invented before us :)

http://www.nennstiel-ruprecht.de/bullfly/fig24.htm

If a bullet flies stable (gyroscopically and dynamically!) and the transient yaw has been damped out, usually after a travelling distance of a few thousands of calibres, the bullet´s axis of symmetry and the tangent to the trajectory deviate by a small angle, which is said to be the yaw of repose .

For bullets fired with right-handed twist, the longitudinal axis points to the right and a little bit upward with respect to the direction of flight, leading to a side drift to the right. The yaw of repose, although normally measuring only fractions of a degree, is the reason for the side deviation of spin-stabilized bullets.

http://www.nennstiel-ruprecht.de/bullfly/fig24.gif

Note that this is fraction of a whole degree, not a fraction of a minute of a degree :)

http://www.nennstiel-ruprecht.de/bullfly/yawrepf.htm

The repose angle of yaw (or yaw of repose, also called equilibrium yaw) is the angle, by which the momentary axis of precession deviates from the direction of flight (see figure ). As soon as the transient yaw induced at the muzzle has been damped out for a stable bullet, the yaw angle d equals the yaw of repose.
The magnitude of the yaw of repose angle is typically only fractions of a degree close to the muzzle, but may take considerable values close to the summit especially for high-elevation angles.

The occurrence of the yaw of repose is responsible for the side drift of spin-stabilized projectiles even in the absence of wind. The spin-dependent side drift is also called derivation.

It can be shown that for right-hand twist, the yaw of repose lies to the right of the trajectory. Thus the bullet nose rosettes with an average off-set to the right, leading to a side drift to the right.


Now at least we can get our terminology in order... :)

From the formula for the yaw of repose (boy, this is a mouthfull, I kinda liked "bullet walk"... :) ) it is proportional to axial (or polar) moment of inertia of the bullet and the rate of spin and in reverse proportion to a forth degree of a bullet speed.... So inconsistent moments of inertia (bullet quality as it leaves the muzzle) and speeds are primary factor in inconsistencies of a "bullet walk", sorry - "yaw of repose" :) Different bullet weghts, shapes, construction - different moments of inertaia - different POI laterally.

Now it would be great to find some numerical /experimental data on actual amount of the efffect...

Some more:
http://www.exteriorballistics.com/ebexplained/5th/42.cfm

And more:
http://www.tuffsteel.com/Ballistics/bullfly/fig25.htm

[Wildfire]

That AA 2230 is good powder and what I use. The 1 in 8 is maybe a little fast for "that" 55 grainer. The 60 sounds much better. If accuracy is what you want, max loads are seldom the accurate ones. The OAL is up to the Magazine. If you are talking about freebore. you may get away with what ever that magazine will allow. As a rule .008 to .015 bullet jump is best, but you gun may not allow that. Yes, the flat based bullets are usually more accurate at shorter ranges. But fail at around the 300 yard mark.
If you are getting 1/2" groups with that bullet stick with it and refine the charge and seating depth. My Varmint rifles are 1 in 14 twist and will not toss a 60 grainer. Faster the twist the heavier the bullet.
Hope I didn't hit the wrong page.

[Walkalong]

ALL bullets wobble a bit until they settle down. Then they must mantain enough rotation to remain stable all the way to the target. The best twist for pinpoint accuracy is one with the slowest twist that will sufficiently stabilize the bullets used for the distance shot. That will settle them down sooner than if they were fired in a faster twist barrel, BUT, a faster twist than necessary barrel can still shoot very, very, well.

Different weight bullets shoot to different points of impact, in general. Nothing mind boggling or strange about it.

Most factory barrels are a bit faster twist than needed for some ammo to accommidate several different bullet weights fired in the same gun at different velocities. They shoot just fine.

[rcmodel]

1. Reloading public somehow decided that they can "time" the bullet speed in the barrel "to catch the barell muzzle" at the point of minimum amplitude. Maybe they are not aware that the physics of the barrel whip *always* makes the muzzle an "anti-node" in deformation waves - the point of maximum whip amplitude and speeds. Then why does the Browning BOSS work so well to tune a barrel?

2. The physics of rifle barrel whip concentrates its energy mostly in the vertical plane This simply isn't true.
Barrel whip can and does occur at any point around the 360 degrees of the barrel.

There is nothing magical about the forces that cause it to only cause it in the vertical plane of the barrel.
A fully bedded barrel or one with only forend tip pressure might be more inclined to move vertically.
A free-floated barrel is free to go any direction the stress in the steel wants to make it go.

But I can see you already have your mind made up, and anything I say isn't going to change it.

Good luck on your quest for the magic bullet that doesn't change the barrel harmonics and stray off POI when you change its weight, bearing surface area, peak chamber pressure, and velocity.

I'm outa here!

http://i81.photobucket.com/albums/j219/rcmodel/KTOG/1224.gif
rcmodel

[FM12]

Take a lesson from the benchrest shooters: up to about 300 yards use, flatbase bullets. The bt dont have time to settle in or "go to sleep" and be stabilized in short (<300 yds) to be as accurate as flat base rounds.

[GlockTerrier]

rcmodel: why does the Browning BOSS work so well to tune a barrel?
I don't own BOSS and cannot attest how well it works beyond the Browning marketing hype, not everything I've read from customers was a success testimony (I personally was skeptical, since the most of potentially useful compensating the whip blast happens a bit late to my taste - *behind* the bullet that already left) - but if it does indeed works well, this only confirms what I said: whip is primarily of a concern to a rifle designer and a rifle construction factor - rather than ammo designer...


Quote(GlockTerrier):
2. The physics of rifle barrel whip concentrates its energy mostly in the vertical plane

Rcmodel: This simply isn't true.
Barrel whip can and does occur at any point around the 360 degrees of the barrel.

Your categorical statement doesn't contradict mine. Yes, the whip does have both lateral and vertical components - but *mostly* the barrel whip in a well constructed rifle is contained in a vertical plane. Which whip your BOSS adjustable muzzle break try to compensate *most* - vertical or lateral?

For example: this patent for muzzle-break device explains the whip very well:
http://www.patentstorm.us/patents/6923292-description.html

The second and third aspect of transition ballistics is vertical and horizontal or lateral barrel whip; studies indicate this event provides a significant psychological portion of perceived recoil by the person discharging the firearm. All gun barrels tend to bend down during rest to a degree determined by their form and rigidity factors. This condition is most prevalent in light shoulder fired firearms; but is also a factor up to cannon bore barrels. Vertical barrel whip is that action that takes place as the projectile moves rapidly through the bore; causing an upward rise of the barrel that attains its maximum the instant the projectile exits the barrel.

Concurrently; rotation of the projectile as defined by the rifling helix imparts a counter torque to the barrel and the vertical vector of this torque amplifies barrel rising whip. Horizontal or lateral barrel whip has a similar effect; but of far less magnitude than vertical whip. Lateral barrel whip is mechanical and is most often caused by poor manufacturing techniques that result in a lateral bend in the barrel and greater attention to barrel manufacturing accuracy can relegate lateral whip to insignificance in actual practice.

If anybody has different sources of data I'd be interested to get a lin to them too...

rcmodel: .. I can see you already have your mind made up, and anything I say isn't going to change it... I'm outa here!

Sorry to see you go, I hope you'd change your mind... :) Certainly, just simply "anything one says" isn't going to change anybody minds... I was just looking to a bit of collective thinking and learning : arguments and contr-arguments based on facts, observations, logic and laws of nature... My mind is not set on anything - I'm just looking for the best and plausible explanations of the facts known to me and observations that I've made myself - and already learned something :) (Peterotte - Thanks!) Spinning bullet's "yaw of repose" is a very interesting effect that may potentially answer some of of my own questions regarding consistent lateral shifts of POI when going from one bullet to another and can be helpful in the bullet selection process.

[Walkalong]

Is Mind F****** a gun related non problem considered gun porn? :evil:
Whoops. I'm outa here too.

[GlockTerrier]

Is Mind F****** a gun related non problem considered gun porn? :evil:
I'd vote: yes - but only by those who have to examine what they use for their brains... :evil:
Thanks for your important contribution to this thread! :)

[peterotte]

2. The physics of rifle barrel whip concentrates its energy mostly in the vertical plane - leaving significant *lateral* POI shifts for different load/bullets completely unexplainable.

I'm glad you mentioned this one, GlockTerrier. My Anschutz shifts its POI laterally 'sometimes'. But, this rifle has a third mounting point just forward of the breach on the barrel. The screw fits into a dovetailed 'nut', which isn't even tight! Or should I say it had a third mounting point. It's gone as of now.

[peterotte]

disneyd , it would be real interesting if you could test those same loads at different distances to see what happens. (Same scope setting of course). Even comparing them to the 60gr at different ranges. If you were able and/or inclined to.:)
Would that be asking too much?

[peterotte]

causing an upward rise of the barrel that attains its maximum the instant the projectile exits the barrel.

That's interesting, GlockTerrier. Thanks for that very informative post!

[GlockTerrier]

For those if us who doesn't terribly mind "gun-related non-problems" I think may be interesing this document:

http://www.firearmstactical.com/pdf/fbi_observer_sniper_manual.pdf
FBI Academy, Quantico, Virginia: "Advanced Rifle Training for the Observer/Sniper"

Although not always technically correct wrt some ballistic effects they do provide some rule-of-thumb data for an effect of imperfections in the bullets:

"A center of gravity displacement of 0.0005" in .308 match bullet can increase group size approximately 1MOA. This is called "radial" error. Axial and radial errors complement each other". Axial error can be induced by non-concentric ammunition or non-square flat bases. Axial error of 0.001 increases a group size ~1moa.

[peterotte]

Just for interest. I have discovered that my Anschutz hornet fore-end sometimes lightly touched the barrel on the side. That would explain the lateral POI shifts I have observed. Fixed it now but need to do some serious range testing!

[Walkalong]

I'd vote: yes - but only by those who have to examine what they use for their brains... :evil:
Thanks for your important contribution to this thread! :)
Thanks. I couldn't resist. :)

[GlockTerrier]

Walkalong: Thanks. I couldn't resist. :)
:) I can easily see that... :) But us geeks also want to have some fun when we're not at the range or the reloading bench :)

BTW, I've spent some more time reading about the bullet flight trying to get a feel for the size of various physical effects..

Alas, it would seem that the "yaw of repose" in ideal bullet by itself is very week effect amounting normally to 0.1MOA at 100 yards and growing to 1MOA at 1000yards for light calibers bullets and is pretty much negligible unless we're talking long-range artillery shell... :)

On the other hand it is my understanding that very little tangible known of effects of "non-ideal" bullets on their flight and effect of its imperfections to static and dynamic stability in flight. My idea of a "bullet walk" had more to do with increased instability in flight due-to imperfections of shape, surface and mass distribution in the bullet that results in increased bullet scatter rather then pure spin effect of rotating ideal bullet's "yaw of repose".

FBI Academy sniper manual cited above gives some sketchy emperical data for these types of the effects but there's no reference to their source or how this was measured.

I have some of these cannelurred bulk 55gr Hornady's. I also have a bullet comparator (ogive-to-base) that I haven't used yet...

What may be interesting to do is to measure anything we can realistically measure about the bullet consistency: OAL, weight, base-to-ogive - for a sizable sample of bulk and match bullets and compare variances, ranges etc. (Granted, we really need to get a rotational momentum characteristics of the bullet - but even these can be better than nothing. )

Then to make three identical loads for three strings of fire:

One - with sorted bulk bullets, sorted to "match bullets" tolerances
Second - bulk bullets selected with typical "bulk" deviations.
Third - close by weight "match bullets".

Shooting and comparing groups from these three strings without touching rifle zero do not prove anything as what we measure is only indirect evidence of potential rotational inconsistencies and is related to the out-of-box bullet rather than parameters of fired, rifle "imprinted" bullet - but still may be interesting as a general idea of the relative importance of bullet parameters consistency...

If anybody made experiments like that already - it'd be interesting to hear what was found...

[Walkalong]

As a Benchrest shooter I can say what we talk about is:

Best Barrel. (Hart, Spencer, Shilen, etc.)

Best Action: (Stolle, Farley, Hall, etc.) Mine's a Rosenthal.

Best Bullet. (Berger, Barts, Knight, Gentner, etc.)

Results on target are all we are interested in, and we are probably not smart enough to figure out how it gets there anyway.

I imagine the High Power shooters know a lot more about those things. We don't care. :)

[GlockTerrier]

Best Barrel. (Hart, Spencer, Shilen, etc.)

Best Action: (Stolle, Farley, Hall, etc.) Mine's a Rosenthal.

Best Bullet. (Berger, Barts, Knight, Gentner, etc.)

Amen to that... :)

However, the subtle point that intrigued me a lot in this discussion was that once one has best his barrel and action thing figured out - one has an ideal platform for experiments and research in rifle-imprinted bullet flight and evaluation.

Want to know how this spinning bullet flies after being imprinted by the rifle and launched? Just fire it from it and you'll see.... :)

Now the geeky reloading question is can we extract more information about the ammo from the results on paper? Is only group size meaningful? What about POI shift, if any? Etc..

[redneck2]

A center of gravity displacement of 0.0005" in .308 match bullet can increase group size approximately 1MOA.
I didn't elaborate, but in the Handloader article, Barsness used a machine that measured bullet quality. Juenke (sp?) maybe. Don't remember now. Anyway, very minor imperfections made for big differences in accuracy.

Just dropping a box of bullets on a concrete floor from the height of a few feet would affect accuracy.

[Walkalong]

Want to know how this spinning bullet flies after being imprinted by the rifle and launched?
Nope. :neener:

Learning to read wind flags is much more important. :rolleyes:

[GlockTerrier]

Quote:
Want to know how this spinning bullet flies after being imprinted by the rifle and launched?

Walkalong: Nope.

:) Real benchresters do not ever check their targets for an evidence where their bullets flight took them - the competion is decided just by reading of windflags... :) Shooting is optional - after all - everybody has best barrels, actions and bullets, so - what would be the point?... :neener:


Learning to read wind flags is much more important.

He-he... ;) Benchresters do know something about bullet flight in the air. Reloaders do want to know even more... :)

[GlockTerrier]

Redneck2:

I didn't elaborate, but in the Handloader article, Barsness used a machine that measured bullet quality. Juenke (sp?) maybe. Don't remember now. Anyway, very minor imperfections made for big differences in accuracy.

Just dropping a box of bullets on a concrete floor from the height of a few feet would affect accuracy.

Was that a hard copy article or is there some online link to it? I'd love to read it...

I also thought that 0.0005" displacements in a soft lead core bullet do not seem too hard to inflict...

[disneyd]

disneyd , it would be real interesting if you could test those same loads at different distances to see what happens. (Same scope setting of course). Even comparing them to the 60gr at different ranges. If you were able and/or inclined to.
Would that be asking too much?

Well, I suppose so, much as I hate to go shooting ;)

I just picked up a box of 55 grain VMaxes, which I'll test against the 55 grain FMJ-BTs and see what I discover.

[peterotte]

Well, I suppose so, much as I hate to go shooting ;)

Great! disneyd, I'll be waiting to here your findings!:)

By the way, how do you folks measure runout? I tried measuring in a lathe then in a holder I made. I held the case by the rim then the bullet and measured the case runout and anything I could think of. I could only detect a small runout at the bullet tip. Meaning that I found the loaded case to be quite straight! Or did I?:scrutiny:

[GlockTerrier]

By the way, how do you folks measure runout? I tried measuring in a lathe then in a holder I made. I held the case by the rim then the bullet and measured the case runout and anything I could think of. I could only detect a small runout at the bullet tip. Meaning that I found the loaded case to be quite straight! Or did I?
Sorry, peterotte - I personally never measured a runout. The idea that geometry measurements may help to estimate imperfections in the bullet having effect during rotation at 300,000 rpm after being fireformed in a more than a foot of a hot steel rifling at 3 speeds of sound just by geometry measurements - always sounded a bit far fetched to me... ;)

But our rifles can actually do that every time to the bullet - no superfast spinning motors required :) I keep thinking that we should be able to improve our reading of the target paper that could tell us everything we need to know about the bullet and ammo, if we know where to look...

Why, for example, disneyd's 55gr not only dispersed but shoot the whole 1.5" -2" higher group at 100 yards from the rifle that can shoot at the same distance the same hole with supposedly better, but close weight 60gr.... Assuming, of course, that disneyd doesn't just pull our leg and didn't just aimed a bit higher.... :)

[Walkalong]

the competion is decided just by reading of windflags...
It is a huge part of it.
everybody has best barrels, actions and bullets
Pretty much. 97% of the rifles/loads on the line are good enough to win. It's the dope pulling the trigger that wins. (while watching the flags ;))

[jpwilly]

My DPMS 20" SS Bull Barrel 1-9 twist will shoot 50-53gr bullets about 1" higher than 60gr bullets. I haven't checked but am sure it has more to do with the velocity difference than the bullet weight. Just got a chronograph but haven't been to the range with it yet. My BBl seems to like the 50gr bullets. I shot some Black Hills Match 69gr and they keyholed at 100yrds!

[peterotte]

Interesting, that, jpwilly . I know that it is unpredictable but one usually expects a lighter and faster bullet to shoot lower. It just goes to show what is going on in a rifle. Is the barrel by any chance lower than the 'recoil' axis?

GlockTerrier, you are right. If I had been more alert I might have 'read' that there was something wrong with my hornet. I just blamed the rusty barrel! And then I got thrown off by one or two very tight groups with different bullets but similar POI.

GlockTerrier, I was thinking more of the effects of a bullet entering the bore 'less than perfectly straight' I am doing stuff to keep it in line as much as possible and my recovered bullets seem to indicate a degree of success but I am not quite sure how to quantify this. And of course there is the all important drop test - the range!:scrutiny:

[GlockTerrier]

I have some of these cannelurred bulk 55gr Hornady's. I also have a bullet comparator (ogive-to-base) that I haven't used yet...

What may be interesting to do is to measure anything we can realistically measure about the bullet consistency: OAL, weight, base-to-ogive - for a sizable sample of bulk and match bullets and compare variances, ranges etc. (Granted, we really need to get a rotational momentum characteristics of the bullet - but even these can be better than nothing. )

He-he... Just wanted to let you know that I was dumb enough actually to waste my time to measure variances of all above factors for two kinds of bullets:

Sierra 52gr MK - and twice as cheap Hornady cannelured 55gr BT-FMJ
The variance/consistency of a three measured factors : weight, OAL, base-to-ogive size - is I think negligible as it is measured in tenths of a percent.

Moreover, much cheaper Hornady 55gr had these miniscule already variances twice lesser than more expensive SMK! [:)]

Although couple of groups don't mean anything - in two 5 shots group (loaded approximately to the similar speed and the same COAL) the best three were the same for SMK and Hornady within 3/4"@100yards from 16" M4gery in semiauto loading mode with Hornady's POI just slightly (0.25") below and to the right from SMK... The biggest difference was with the "unlucky" 2, though :) My SMK's "flyers" increased 5-shot group just to 1.25". My Hornady unlucky 2 were way off center - about 1-2" to the right and higher... I'm writing these off as just me being a lousy shot - as I don't have any other explanation, since I was shoothing through the chrono... :)

(But I could swear that my POA at no time was even close to these far away (at 8x scope magnification) points :) )

I'm convinced now that all these "easy" bullet parameters is a waste of time to measure - as they do not provide any insights into consistency of much more I think important parameter of the spinning bullet in flight - its mass distribution.

So what is a popular wisdom, guys - have you seen "flyers" that suprised you, ones you couldn't "call"? Is this always an "operator error" ? Or can the "flyer" be just a seriuos anomaly in the bullet flight?

[taliv]

flyers are exactly that by definition: ones that surprise you and that aren't on call.

what most people call flyers, are actually just the result of a normal group with insufficient sample size.


edit: there's a sticky on arfcom that adequately describes the phenomenon. if you havent' read it, let me know and i'll find a link.

[GlockTerrier]

there's a sticky on arfcom that adequately describes the phenomenon. if you havent' read it, let me know and i'll find a link.

Thanks! I'd appreciate that very much!

I think I understand random distrubitions, bell curves, "three sigmas", etc..
I'm just curiuous if there's a sense of relative contrubutions to this "randomness" of various factors in a "typical group" - say, bullet flight anomalies (random shift of POI for fixed POA/launching charachteristics) vs. "bad shooter" factor (random sfift in POA resulting in POI shift)...

[peterotte]

there's a sticky on arfcom that adequately describes the phenomenon. if you havent' read it, let me know and i'll find a link.

I would appreciate that too. Thank you!:)

I fired a few five shot groups and what surprised me was the tendency for there to be 3 shots close together, one a bit further away and a 'flyer' printing high (or sometimes, elsewhere). These were with different bullets and charges. The general POI was similar. (There was some gusty wind but at 100m/110yds)? Unfortunately, I couldn't see the holes so I do not know the order of the strikes.

[taliv]

http://arfcom.com/forums/topic.html?b=3&f=118&t=279218

[Walkalong]

what most people call flyers, are actually just the result of a normal group with insufficient sample size
Usually just a misplaced shot, called or not. :D

Sometimes there are unexplained "fliers" which experienced rifle shooters can differentiate from a missed shot.

[GlockTerrier]

http://arfcom.com/forums/topic.html?b=3&f=118&t=279218

Thank you very much, taliv!

There was not a whole lot of a new or interesting information for me wrt statistical group measurements, my college professors many years ago made sure that I never forget such basics :)

However, I found a quote there from Rick Jamison who actually built and used a "machine rest" to exclude a shift in POA due to an "operator error" that was exactly what I was looking for:

There are stories of a single bullet that for no explained reason flies out of what might have been a tight cluster. This often occurs with a three-shot string and many times with a five-shot string. If you're lucky enough to fire a group without a flier, you can end up with a very tight group. However, usually what happens if another five or seven shots are fired to complete a 10-shot string, other bullets fill in the space between the main group and the flier to make a reasonably rounded group. Ten shots are a more reliable indicator when it comes to predicting what a load is likely to do in the future.

The problem with 10-shot groups is that when you report them, everyone thinks you aren't shooting very well or that the ammunition is not good because the group sizes are so much larger than three- or five-shot groups. Also, when we're firing three- or five-shot groups with a flier, it is only natural to assume that it was caused by a flinch or "pulling" the shot. Therefore, since the flier was our own fault, the tendency is to eliminate it from any reporting of group size.

This is one of the advantages of using a machine rest... The machine rest reduces the human element.
After using this machine rest for several years, I have determined that a 1.5-inch 10-shot group at 100 yards... is a good one.

If which case a "flyer" can still be most often exactly that, after all - a deviation of a bullet in flight... :)

[GlockTerrier]

Usually just a misplaced shot, called or not. :D

Never doubt your word, Your Honour - but out of sheer curiousity - how do you know that? :D

[taliv]

you're welcome. yeah, the article wasn't very technical, and it's maybe a little overbearing/insulting. but, that's arfcom for you.


If which case a "flyer" can still be most often exactly that, after all - a deviation of a bullet in flight...


i don't understand your point. it's not ANY deviation. it's an unexplained deviation. if i pull a shot or jerk the trigger, that's not a flyer. it's a bad shot.

really, a flyer is just something outside your normal group that's not accounted for.

the point of that link is that if you eliminate as many of those human factors as possible and shoot sufficient sample size, most people's rifle/ammo combo are going to be doing good to achieve 1.5 inch groups. it's not flyers that make it a 1.5 inch group. flyers are outside that.


imho, bonafide flyers are probably due to things like a small, off-center bubble in the bullet core, or the bullet having been seated crooked, and me too lazy to weigh/check runout. or maybe something caused the last bullet to leave a little extra piece of copper fouling in the barrel and that affects my next shot. who knows?

[peterotte]

Thanks for that taliv. To illustrate that point exactly, you can have a look over at this link to see my 3 shot groups ;).
http://www.opticstalk.com/forum_posts.asp?TID=8183&PN=1&TPN=4
Next, I'll be posting the full five shot groups - including the 'flyers' :evil:

[GlockTerrier]

i don't understand your point. it's not ANY deviation. it's an unexplained deviation.

I think the rest of your post tells me that you've got my point pretty good. :)

Only "machine rest" or other some like contraption is capable to eliminate "human factor". Nothing else. Note that 1.5" out of 10(!) from "machine rest" is a good(!) group in 100 yards.

And if you waded through the statistics portion of the thread you'd agree that if your one "good" 10 shot group is 1.5", your "bad" 10 shot group can be 4.5" - from the machine rest. :) No human error invoved. :)

Assuming that launching platform and ammo loading characteristics and components are nearly identical - only bullet flight properties would be different. I call it a "flyer" :)

[peterotte]

'Flyers' would be an impact that is obviously and substantially out of place in a ten shot string. They could indicate muzzle wear or throat erosion. You guys actually bring up an interesting and very relevant point here. That is strike probability. Wouldn't it be better to quote accuracy in terms of how many out of ten shots would fall within MOA? Say, 75% MOA, 90% 1.5 MOA, 100% 2 MOA. That means that at worst, my shot will fall within 4" @ 200yds but 75% of my shots will be within 2". Make any sense?

I used to use the three shot group for sighting in purposes. I knew my rifle would print a certain 10 shot group size. So, to adjust my sights, I would fire a three shot group, assuming that the spread would represent the group. If those three grouped too close together, I knew I had not found the mean group centre - but only because I knew the 10 shot group size. To me, that's and accurate rifle. One that shoots a three shot group that represents the mean. (Funny thing - I found 1.5 MOA 10 shot string, to be a good group too. From a machine rest, that is. But my 303 did better, with 50mm at 200m – at least, I think that is better. At that distance, I could hit a beer can).

[GlockTerrier]

Wouldn't it be better to quote accuracy in terms of how many out of ten shots would fall within MOA? Say, 75% MOA, 90% 1.5 MOA, 100% 2 MOA. That means that at worst, my shot will fall within 4" @ 200yds but 75% of my shots will be within 2". Make any sense?

Makes perfect sense to me, peterotte! In fact you've just formulated pretty much a definition of a probabilty distribution function from statistics... :) I keep this type of description in my head as an aggregate description of my accuracy - like, at this distance with this ammo I can hit this area this number of times out of that on average.... Helps to plan ammunition count required to hit the target :)

The question for a reloader is what do we do in the absence of the "machine rest" contraption to separate ammo/rifle issues from the "human factor? If once in a 30 shots the ammo can fly 4.5" off the POA even from a machine rest - whose fault this 4" flyer is on this specific 3, 5, 10, 30 shot group? Given two types of ammunition and no "machine rest" how soon can we tell with a confidence that one is better than the other?

[peterotte]

Good point GlockTerrier . My problem as I see it is to find out what might have caused a flyer so as to eliminate that cause. That's what makes it fun - and frustrating! I shot a few groups of five of different loadings this weekend past and found a tendency for the rifle to print three very close, one a bit off, and another way off high. Does that mean I have a crap rifle or is there some inconsistency with my loads? Only one way to find out - keep trying! The only thing I am sure of is that those bad shots were not me.:)

By the way, I concluded on the machine rest thing that I can shoot as well without one, from a bench so gave up on it. (I even had a little hydraulic trigger device to fire it).

[Walkalong]

tendency for the rifle to print three very close, one a bit off, and another way off high
Shoulder, breeze switching and blowing towards the target, bedding, you. :scrutiny:

It is consistent, so I would not call it a flier. It is not unexplainable, just not diagnosed yet. :)

I think we define "flier" differently. Most "fliers" are not fliers by my way of thinking. It is not a statistical anomoly, it is an occasional unexplainable random shot away from the statistical group.

[GlockTerrier]

I concluded on the machine rest thing that I can shoot as well without one, from a bench so gave up on it. (I even had a little hydraulic trigger device to fire it).

Peterotte, with all respect, I think you had probably a very solid but still a shooting rest for your rifle... ;) It greatly diminished but did not exclude completely POA variability from shot to shot. But have you seen Ricks' "machine rest" contraption ? It is no rifle anymore - it is some kind of action merged on a massive platform, pretty much just a lunching platform for bullets:

http://www.box.net/shared/static/zsil47gbhq.jpg

If THIS thing calls 1.5"@100y in 10 shots a "good" group, this statistically means that you have a decent chance to a 4.5" miss when shooting several 10 shot groups - due to a variance in bullet flight trajectory alone!

No wonder that you shoot as good w/o the rest as with it - it can easily be explained if your error contribution to "flyers" is probably less than variance of bullet trajectories due to variance in bullet/ammo properties and their interaction with environment in flight - wind, etc.

[GlockTerrier]

I think we define "flier" differently. Most "fliers" are not fliers by my way of thinking. It is not a statistical anomoly, it is an occasional unexplainable random shot away from the statistical group.

Walkalong, naughty you, you're on the verge of crossing into philosophical porn about scientific method, randomness, determinism, etc. :) Out of all people here... :)

Statistics as method comes into play when gazzilion of physical factors that deterministically define every individual outcome - are all lumped together, so instead of attempting predicting inidvidual outcome we're content to describe the approximate behavior of the large group of observations influnced by the same gazillion factors (averages, deviations and other such properties)

Here you have it - if you have a statistical method, you're NOT interested in explanations of every individual observation by definition. You're mostly studying properties of large collections of these observations and how these aggregate properties may statistically correlate with a few selected factors.

But if your looking for an explanation why this specific hole punched 4" off center - statistics (group sizes, etc) are meaningless. You're right into detailed examination of the physics and laws of the phenomen you study....

So depending on the method a "flyer" is just a sample from a "tail" of a random distribution. Or it is an interesting trajectory of a specific bullet flight that takes it farther way from a theoretical/expected POI for the same POA and other initial flight charcteristics as the other bullets - that we're trying to explain away. :)

[peterotte]

OK - that was hard to follow but a lot of fun!:)

You are right GlockTerrier. What I had was a device, which supported the rifle, free of human hands. The rifle was sighted by moving the whole contraption on jacking screws. I built it to be similar to being held by a human. The hydraulic trigger was to eliminate any trigger let-off influences.

The 'machine rest' you show puts 'machine' into machine rest! I used mine primarily for sighting in and of course, developing loads.

Walkalong, my idea of a flyer is an indication of some correctable error that could either be a defective load or a defect in the rifle or it could be wind or that undetected flinch! OR - even worse - it could be the random scatter that the rifle and load normally produces! But of course, you are right!

In my case, with my hornet, I am getting a five shot group pattern which is puzzling because it has the same general pattern, in the same general place. That makes me think there might be hope for the rifle if I can find a good load for it. (I know I have found a bad load for it - seven shots placed all over an A4 page at 100m)!:barf:

There was a wind but I am kinda reluctant to just 'blame' that, or I might miss the true cause.

[OLD DOMENION]

I had a Ruger Ultra-Lite that, when I called Ruger said it was a 1 in10 twist. I did the following and found it was a 1 in 12 twist:
Start a tight patch; being sure the jag is tight on the rod.
Mark the rod with a felt tip to indicate Top Dead Center and a starting point.
Advance the rod until it comes back to Top Dead Center.
Measure the distance traveled from the start mark. That is the rifling twist, one turn in xx inches.
A lot easier than trying to estimate the amount of twist in a foot.
This took my group from a 3 1/2 inch group down to a dime size. Of course I needed to downsize the little Ultra-Lite's load from 3200 to 2600 feet per second.

[peterotte]

OLD DOMENION , you say you had to reduce your load to tighten your group?! That's interesting. Just this weekend, a guy in the gun shop was saying something similar, and I was wondering about it. What bullets were you using and what powder?

On a side note. I have been reading for some time now that a hornet needs a good 'crimp' to get best accuracy. Well, I have been using no neck tension at all (unsized cases) and have found no difference, until now. I was expecting it so prepared for it - with Hodgdon's Lil'Gun, good neck tension is essential for good ignition. Not so with AR2205(H4227). Something else I found - 55gr Hornady Spire Points shot all over the place (but nose first) while 55gr Nosler Boat Tail Spitzers with the lead tip cut off, shot reasonably well - even though bullet yaw was evident on the target. (My hornet has a 1 in 16 twist)! :confused: Because I have no intensions of crimping, I have made myself a neck sizer die that increases neck tension and does not require an expander plug.

Of course, none of this may be of interest to disneyd, but there might just be a relationship. Bullet jump perhaps? I intend trying out the same bullet with different powder (Lil'Gun) and with less AR2205(H4227) and more jump, just to see what happens.

[GlockTerrier]

I had a Ruger Ultra-Lite that, when I called Ruger said it was a 1 in10 twist. I did the following and found it was a 1 in 12 twist...I needed to downsize the little Ultra-Lite's load from 3200 to 2600 feet per second.

This is interesting.... If you have a lower twist rate than necessary to stabilize the bullet this means you may need to increase its speed to get a spin required to stabilize the (longer/heavier) bullet.... Perhaps the problem lies with a damage of thin jackets of a lightweight bullets... These have been known to disintegrate in the air at high velocities from fast-twist barrels. Even w/o disintegration, the damaged jacket can significantlly alter and randomize the flight trajectory. This may explain an effect the lowering the speed had on your bullets. As your barrel rifling ages (getting less "sharp") you might notice that you can get more more speed with lightweight bullets w/o ill-effects on accuracy...

[disneyd]

Finally made it back out to the range... the short story is that it's the bullet quality and not the weight that was causing the discrepancy.

I shot the 55gn VMaxes at 100 yards and they shot almost as well as the 60gn VMaxes. The 55gn FMJ-BTs produced the same group that they did earlier (the one I posted pics of).

Shot all the loads at 50 yards also. No surprises there except that the 55gn FMJ-BTs didn't tighten up as much as I thought they would (about 1.5" at 50 yards vs 2" at 100).

[Walkalong]

Quote:
Originally Posted by Walkalong
Usually just a misplaced shot, called or not.

Never doubt your word, Your Honour - ?
Your Honour! I'm flattered. :neener:
but out of sheer curiousity - how do you know that
Experience. Lots of shooting. 250 to 300 shots in a weekend in competion where every shot counts can really put you in tune with a rifle.

Walkalong, naughty you, you're on the verge of crossing into philosophical porn about scientific method, randomness, determinism, etc. Out of all people here...
Nah, just saying fliers are unexplainable.

Walkalong, my idea of a flyer is an indication of some correctable error that could either be a defective load or a defect in the rifle or it could be wind or that undetected flinch! OR - even worse - it could be the random scatter that the rifle and load normally produces!
I disagree. You are talking about a bad shot that can be fixed, not a flier.

[peterotte]

Shot all the loads at 50 yards also. No surprises there except that the 55gn FMJ-BTs didn't tighten up as much as I thought they would (about 1.5" at 50 yards vs 2" at 100). up

disneyd - that is interesting. Maybe those groups will tighten up further downrange? But at least you know it is not the rifle!

Nah, just saying fliers are unexplainable.

I disagree. You are talking about a bad shot that can be fixed, not a flier.

True, but then again, a flyer is an unexplained out of group shot. Not unexplainable.:) (But I would expect it to be quite far out of group).

But one thing is for sure - only ten shot groups count! (Actually, it's amazing how those 'flyers' seem to just blend into a ten shot group)!;)

....... the damaged jacket can significantlly alter and randomize the flight trajectory. This may explain an effect the lowering the speed had on your bullets......

That makes sense - I never thought of that!

But why would someone say a slower twist requires a heavier bullet? (In my case the guy was talking about the hornet). Maybe he just got confused? Or maybe he meant a shorter bullet of the same weight?

[GlockTerrier]

Shot all the loads at 50 yards also. No surprises there except that the 55gn FMJ-BTs didn't tighten up as much as I thought they would (about 1.5" at 50 yards vs 2" at 100).

This clearly points to a lack of a dynamic stability in a bullet flight.

The physics of the spining bullet flight is that right after leaving the barel the spinning bullet "corkscrews" witin 1-2moa for about 7000 calibers (0.224" * 1000 = 224" ~20ft) length of flight. With dynamically stable bullet these oscilations will dampen as flight progresses further on - w/o it they will go on to keeping its 1-2moa corckscrew trajectory for a duration of the flight - giving you a scatter gun pattern of that size on the paper....

Dynamic stabilty for a given spin rate and a speed if I remember correctly depends mostly on mass distribution, a shape of the bullet and magnitude of various destabilizing forces (like the Magnus effect ("spitball effect") that damaged jackets could significantly increase for the bullet)

[disneyd]

Glockterrier.... would you assume that the FMJ-BTs that I'm using are not balanced well? (non-uniform density?)

[Walkalong]

But one thing is for sure - only ten shot groups count! (Actually, it's amazing how those 'flyers' seem to just blend into a ten shot group)!;)
If it is blending into the group it is not a flier. I am talking about 5 shot groups. A plenty good enough test of load and skill.

True, but then again, a flyer is an unexplained out of group shot. Not unexplainable. :)
You are missing the point. The unexplainable out of the group is a flier. The explainable, whether you can figure it out or not, is not a flier. I will say it again, most so called fliers are not fliers, but just bad shots which the shooter can not explain, or is unwilling to take responsibility for. ;)

[peterotte]

...most so called fliers are not fliers, but just bad shots which the shooter can not explain, or is unwilling to take responsibility for
Or just chooses to reject as it spoils our groups!:evil: Or is that the same thing?:D

I fired a five shot group and had three shots hit at 0.3 MOA, the forth opened the group to 0.7 MOA and the fifth to 1.2 MOA. That last one 'looked' like a flyer but was really one of the shots that would 'blend in' in a 10 shot string. (But since it was high, it could have been a bad load.:confused:)

I still think of the percentage thing. Like 25% falling within 1/2 MOA, 75% falling within 1 1/4 MOA and 95% falling within 2 MOA while 5% might be as bad as 3MOA. So when taking a shot in the field, it would wise to take that possibility into account.:scrutiny: Someone once pointed out that it only matters where the first shot falls!:p

No-one should ever say our sport is dull!:)

[peterotte]

...most so called fliers are not fliers, but just bad shots which the shooter can not explain, or is unwilling to take responsibility for
Or just chooses to reject as it spoils our groups!:evil: Or is that the same thing?:D

I fire a five shot group and had three shots hit at 0.3 MOA, the forth opened the group to 0.7 MOA and the fifth to 1.2 MOA. That last one 'looked' like a flyer but was really one of the shots that would 'blend in' in a 10 shot string. But since it was high, it could have been a bad load.:confused: Other five shot groups produced similar results in a similar POI.

So, realistically, do I include that fifth shot for sighting in or should I use the four that clustered fairly close together?

I still think of the percentage thing. Like 25% fall within 1/2 MOA, 75% fall within 1 1/4 MOA and 90% fall within 2 MOA while 10% might be as bad as 3MOA. So when taking a shot in the field, it would wise to take that possibility into account.:scrutiny: Someone once pointed out that it only matters where the first shot falls!:p

No-one should ever say our sport is dull!:)

[Walkalong]

So, realistically, do I include that fifth shot for sighting in or should I use the four that clustered fairly close together?
The first four, of course. If it it always the 5th shot it could be as simple as the barrel heating up and changing the point of impact. For hunting that 5th shot is meaningless anyway.

For target shooting, it is huge. Now we need to know what is causeing it. Load? Shooter? Barrel? etc. If it is random it REALLY needs to be fixed. If it is me I can rest easy about my rifle/load and concentrate on my shooting to eliminate it. That is a big part of target shooting. Diagnosing problems so we can fix them.

I was shooting a match outside Atlanta at Riverbend a long time back when the shooter next to me was having a lot of trouble. He was a real good shooter, but was just having fits. he decided it was his new set of brass. He was going to ditch them. I told him I did not think it was the brass, but he insisted. I took his brass and beat him with it in my gun the next two matches (next 2 5 shot groups). he had a fit and screwed his barrel off of his gun and chucked IT in the trash. His equipment was fine. He was just frustrated and unwilling to admit to himself that he was just having a bad day shooting and that his equipment was fine. We all have those days. One day we are world beaters and the next day we S***. :)

If you are going to shoot competitively, especially in Benchrest, you better be ready to eat a lot of humble pie. They told me that when I started and they were right. :D

[peterotte]

Thanks for that Walkalong , that was helpful and encouraging.:) I must say, when I see what others are producing, I get a little daunted.:uhoh: Competition really isn't easy! (But a great bunch of guys). I used to shoot 22lr silhouette at club level. I got real good. Growing up with a rifle in my hands bore fruit. Now, twenty years later, I am trying to pick up again. Well, what can I say?:( At least I still have my tropy.:)

[Walkalong]

Keep at it. You'll knock the rust off soon enough. :)