Help figuring out .223 accuracy discrepancy

[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]

well...

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?



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.

 

[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.

 

[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]

.223 discrepency

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..


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.


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.


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.


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 exist

Again, 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?


rcmodel