[Varminthound]

Has anyone experienced this? While developing loads for my Bushmaster (.223) I was shooting 5 shot groups. To speed things along I loaded 10 rounds (of the same load) and fired five at each of two targets. I did this repeatedly. I realized that the first five rounds consistently gave smaller groups. I was slow firing so barrel heat wasn't building up. My feeling is the magazine spring is more consistent when fully compressed for the first five rounds.

By the way, this happened with different powders and bullet weights when tested, so it wasn't just a one time event.

Rifle also likes aftermarket mags better than the Bushmaster mags when I look at the results on paper.

Thanks for any help or comments.

[rcmodel]

I can think of no reason the magazine could have any effect at all on AR accuracy.

It could be you are just getting mentally tired before you get done shooting two 5-shot groups in a row, and the groups start to suffer.

Or, your barrel is getting hotter then you think it is.

To prove or disprove those theories, shoot one shot on each target, and repeat until all 10 rounds are fired.

The two groups should be identically good, or bad.

rcmodel

[mkl]

Like rcmodel, I can't think of anything the magazine would have to do with your experience. I have a Bushmaster with the target barrel and have never run into your problem.

Only thing I can think of is that perhaps you do not have enough neck tension on your handloads, and the recoil or feeding cycle is changing the overall length of your cartridges.

Try loading ten cartridges in your magazine that you have verified are the same OAL. Shoot the first five and then carefully unload the rest of your magazine and measure the OAL. If it has changed, you need more neck tension.

Other than the above, I'm at a loss to think of any reason groups would change other than barrel heating which you say is not happening.

[rcmodel]

I was also thinking short OAL load length causing recoil battered soft-point bullet tips.

But I doubt that would have much if any affect on group size as the point shape is non-critical anyway.

rcmodel

[mkl]

I wasn't thinking bullet tips, but changing case capacity/pressures, or distance to the leads. If his bullet is moving in/out of the case as a result of recoil/cycling, he would be shooting a different dimension cartridge each time he pulled the trigger.

I think the last five in the magazine would be more prone to this effect than the first five because of the gun's tendency to pivot around its center of balance during recoil.

[rcmodel]

I agree.
And the last five get hit five to nine more times then the first five.

rcmodel

[cpttango30]

Sounds like you need to add a little bit more crimp on them loads.

[rcmodel]

Actually, a little more neck tension would be better.

Crimp if you must, but neck tension alone should keep the bullets from setting back in the magazine on anything less then an elephant gun.

rcmodel

[taliv]

perhaps too much crimp is what's causing not enough neck tension?

[mkl]

Sounds like you need to add a little bit more crimp on them loads.

Crimp is seldom the problem, especially in a 223.

If the bullets are moving in a gun with as light a recoil as a .223, the problem is neck tension, not crimp.

I never crimp my 223 loads, and have yet to have one move as a result of firing.

Actually, although I reload for seven or more rifle cartridges, including the 30-06, I only crimp in one cartridge -- my 45-70 with 405 grain bullets and high power loads.

With the exception of my 45-70, I have never had a rifle bullet moved because of recoil. Without any crimp my 22 Hornet, 30-30 Winchester, 243 Winchester, 6.5x55 Swede, 30-06, 7.62x54 Russian, 303 British, and a few others in the safe I can't remember right now have never moved a bullet under recoil even though the bullet was not crimped.

Crimp is not the answer to 95 percent of bullets moving -- it is neck tension. If the neck tension is not correct, heavy crimping will not only not fix the problem, it will make it worse.

My experience after 40+ years of reloading FWIW.

[DaveInFloweryBranchGA]

I'm with rcmodel and mkl on this one. Fix the neck tension.

Regards,

Dave

[snuffy]

If the bullets are moving in a gun with as light a recoil as a .223, the problem is neck tension, not crimp.

I'll go one further. The barely perceptual recoil of an AR just won't move a shell in a magazine. I just can't see it happening. if the round is not moving, it can't contact the front of the mag to affect the depth of the bullet. Possibly if only 3-4 rounds are in a 30 round mag, then they're left with sizing lube on them, then they may move a little. But enough to seat a bullet deeper? Prove it!

[Varminthound]

Thanks for all the comments and suggestions. As soon as I can get back out (hopefully tomorrow) I'll post and let you all know what happened.

[Varminthound]

Made it to the range today.

Measured the OAL of the first five and then loaded 5 more on top. After firing the top 5 I carefully removed the remaining 5 and measured. As many of you figured out, the OAL had changed. The changed was .0010 to .0015 in 60 percent. Enough to raise the pressure and change the point of impact.

None of the rounds I have been firing were crimped so the neck tension would almost have to be the cause. This ocurred with different loadings.

So now I will get to work and determine the buhing I need when I place an order for Redding dies.

I am always open to suggestions and thank you for the assist.

Hopefully, this will prove instructive to more than me.