Help figuring out .223 accuracy discrepancy

[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)!

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

 

[OLD DOMENION]

Verify that .223 twist

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)! 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]

Update

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.

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! Or is that the same thing?

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.)

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. Someone once pointed out that it only matters where the first shot falls!

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! Or is that the same thing?

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. 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. Someone once pointed out that it only matters where the first shot falls!

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.

 

[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. 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.