Question on accuracy - extended mags in semiautos

Jmoser

Jmoser

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Maybe a question for the M1A folks - I have heard that different mags can impact accuracy if they put different pressure on the bolt etc. from underneath?

Shot some good handload groups in my BAR Mk 3 [FN style] but then had some crazy flyers - didn't occur to me later that I may have been pushing the mag/magwell against my oversized front rest sandbag. This extended mag could have been under pressure - bag pushing the bottom front back and top rear up; maybe this is an issue?

Of course next range trip I will pay attention to this but just curious how severe this can be in different rifles; never seen it in AR platforms even using 30 rounders as a monopod off the bench.

Thoughts?
 
I've not noticed any difference shooting 5, 10 or 20 round magazines in the M1a. Back when I had the FNAR I never tried the 20, but the 10 and 5 were same length...a 5 was a 10 with a dimple to limit the follower. What I did do was shoot it "monopod" propped up on the 10 rd magazine off a branch that was a convenient height. It didn't make me miss, but I wasn't shooting groups either. So little help to offer, but what do you mean by flyers? A half inch group opens up to an inch, or it open up to three inches?

I'm thinking the bolt cams shut on the Browning BAR. That should prevent much movement I'd think. I can see where pressure under the bolt might affect a 10/22 or blowback action 9mm.
 
I have considered this before, but mostly with fully loaded magazines, the ones that can be hard to seat. This would imply considerable pressure on the underside of the bolt/slide, both statically and dynamically. I would think this could impact the fit and function of the gun to some degree. Conversely, as you reach the end of a magazine, there could be a significant drop in bearing pressure and again affecting fit and function. Actually, I've seen magazines vary in pressure, both up and down as it moves from full to empty.
But, this is conjecture on my part. I'm not familiar with demonstrative examples of this as a problem.
But, personally, I never "top off" magazines anymore, especially if they are hard to seat when "full".

just my .02
 
Personally I doubt this could have caused the flyers - just chasing down ideas. Shot a good group with the same load before so could just be one of those days. I was loading 5 rounds - had thought of the varying follower pressure.

Try again with different rest setup and report back, appreciate the feedback.
 
Jmoser said:
Personally I doubt this could have caused the flyers - just chasing down ideas. Shot a good group with the same load before so could just be one of those days. I was loading 5 rounds - had thought of the varying follower pressure.

Try again with different rest setup and report back, appreciate the feedback.
Click to expand...

You try Single shot?
 
YeeHaa said:
You try Single shot?
Click to expand...
Ya - thing about that - spent lots of time and $ working up single shot MOA load for my FAL, turn the gas block on and 6" vertical strings.

Have a .308 semiauto and I want to get it running that way. Sold my Encore already . . . want a repeater ;)
 
Jmoser said:
Ya - thing about that - spent lots of time and $ working up single shot MOA load for my FAL, turn the gas block on and 6" vertical strings.

Have a .308 semiauto and I want to get it running that way. Sold my Encore already . . . want a repeater ;)
Click to expand...

If your concern is to determine if a magazine will effect accuracy, ( Auto Loader or not ) then you misunderstood what I was suggesting.

Leave any adjustments, ( i.e. Gas or whatever ) set for normal auto loader operation and do not insert the magazine.
This means just load single rounds into the firearm and it will remove the Magazine Factor.

If you are just looking for opinions I don't have one.

I can share that I have experienced magazine issues that have effected grouping ~ accuracy in more ways than just having a magazine inserted, BTW to include a FAL as well.

Hope you figure it out. ;)

Safe Shooting
 
I shot the M1A competitively for a number of years. I never noticed any significant group shifting between mags, but I was using all USGI mags... no aftermarket.

My old HP mentor did tell me that he would test multiple mags to see which two shot the same POI and then "marry" them as a matched pair, for the sole purpose of shooting the rapid rifle strings. He was an accomplished shooter that could really drive an M1A/M14 hard, so I believe that there was truth in his words. At the time, I could never hold hard enough in the rapids to be able to tell.
 
nbkky71 said:
I shot the M1A competitively for a number of years. I never noticed any significant group shifting between mags, but I was using all USGI mags... no aftermarket.

My old HP mentor did tell me that he would test multiple mags to see which two shot the same POI and then "marry" them as a matched pair, for the sole purpose of shooting the rapid rifle strings. He was an accomplished shooter that could really drive an M1A/M14 hard, so I believe that there was truth in his words. At the time, I could never hold hard enough in the rapids to be able to tell.
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I ASSUME you had dual recoil lugs, bedded action and a fiberglass stock.

If my assumptions are correct, I THINK that match condition on your firearm might help with variables. Like mag height / bold touching, etc.

I have some odd stories about what it took to make a M21. The story you tell falls right in line.

Thanks for sharing.
 
@Jmoser

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