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Posted: 4/8/2014 5:56:08 PM EDT
| I had an interesting question today form a friend of mine regarding a change in rifle accuracy, with a change in magazines. He said he was shooting with XM193 using Pmags and getting reasonable accuracy at 50 yards, around 1 inch groups. He changed to USGI mags, shooting the same XM193 and noticed his group size double. I recognize that it is not easy to dissect with third hand information but that's all I have. Have any of you ever experienced a change of accuracy by simply changing mags? |
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My guess is that there are several more unaccounted-for variables floating around.
Unless something is deforming the tip of the bullet when it is fed, I can't imagine how the magazine could change group size. Have him remove the magazine before each shot, and reload from an open (locked back) bolt and see what happens. Once the bolt closes, the magazine is irrelevant. |
| P-mags do have grooves in front where the rounds slide out . GI mags do not & can remove some material from the projectile. Maybe file that area down a bit & see what happens .I noticed this on some of my GI mags & filed them down just to feed smoother, never checked for accuracy. |
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On some rifles, like FN-FALs, the bolt locks at the rear, and as the magazine empties it puts less and less pressure on the bottom of the bolt. This can effect accuracy. On the AR, it locks up in the receiver extension. Your friend is broken. Not only that, but the rounds in the mag don't even push on the bolt at all; they push on the carrier. If the bolt has a good lock-up in the barrel extension, I can't imagine the carrier tilting it too much. |
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My guess is that there are several more unaccounted-for variables floating around. Unless something is deforming the tip of the bullet when it is fed, I can't imagine how the magazine could change group size. Have him remove the magazine before each shot, and reload from an open (locked back) bolt and see what happens. Once the bolt closes, the magazine is irrelevant. Even if the GI mag is somehow beating the heck out of the bullet nose I wouldn't expect to see much difference at a 50 yard range |
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Before yesterday I would have said no or very little effect from a mag BUT
Yesterday I was shooting my new 300blk at 100 yards off an Atlas Bipod legs down one notch so I would not rest on a mag base. Shooting 168 smk RL-7 handloads with a 20 rd Gen 2 Pmag I was getting severe verticle stringing, for the last 5 round group I used a C Products 30rd got a centered 1 1/2 group (that was the only change in 4 strings) The P Mag also would (2 different instances) strip a round out of the mag push it into the chamber but the bolt would not be snapped on the cartridge This Rifle shoots well with C Products, and when the rounds stay put with Lancer L5 but did not care for the Gen 2 P Mag at all |
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IDK, but it is a widely accepted fact that the first hand cycled round in an auto pistol will sometimes be a flyer from the rest of a string fired from the mag. Has something to do with stripping and seating force .
http://www.ar15.com/forums/t_3_66/332932_.html |
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Quoted: IDK, but it is a widely accepted fact that the first hand cycled round in an auto pistol will sometimes be a flyer from the rest of a string fired from the mag. Has something to do with stripping and seating force . The first round through a clean/oiled barrel may fly a little differently from subsequent rounds but I've never once had a problem with the first round from a magazine after the barrel is fouled by any previous shooting. |
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In all my years, I've never heard that tale. The first round through a clean/oiled barrel may fly a little differently from subsequent rounds but I've never once had a problem with the first round from a magazine after the barrel is fouled by any previous shooting. Quoted:
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IDK, but it is a widely accepted fact that the first hand cycled round in an auto pistol will sometimes be a flyer from the rest of a string fired from the mag. Has something to do with stripping and seating force . The first round through a clean/oiled barrel may fly a little differently from subsequent rounds but I've never once had a problem with the first round from a magazine after the barrel is fouled by any previous shooting. Sorry you haven't heard this, but it is true and not a tale. It's old news in the pistol world. First round mag flyers are common. |
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I had an interesting question today form a friend of mine regarding a change in rifle accuracy, with a change in magazines. He said he was shooting with XM193 using Pmags and getting reasonable accuracy at 50 yards, around 1 inch groups. He changed to USGI mags, shooting the same XM193 and noticed his group size double. I recognize that it is not easy to dissect with third hand information but that's all I have. Have any of you ever experienced a change of accuracy by simply changing mags? Ain't gonna happen. Magazines will have no effect on accuracy whatsoever - UNLESS they are damaging the bullet on the way out. Seems unlikely, but you never know. |
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It didn't happen.
The mere fact this is seriously being discussed as a possibility is mind boggling. In all the rifles I shoot, the accuracy of the projectile is dictated by the barrel, the inherent ballistics of the round, and the weather(environment). With all of those three items being consistent, you should see consistent results. If not... User error. |
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IDK, but it is a widely accepted fact that the first hand cycled round in an auto pistol will sometimes be a flyer from the rest of a string fired from the mag. Has something to do with stripping and seating force . http://www.ar15.com/forums/t_3_66/332932_.html I've always heard the first round might be a flyer due to the barrel not up to 'optimum operating temperature'. Not saying that's wrong, just never heard it before. As far as magazine affecting accuracy, unless it's severely defective I'd sooner blame a stray crosswind or shooter skill over a magazine. I've tossed some pi$$ poor mags in the trash cause they weren't reliable, but when they worked I never noticed any affect on accuracy. |
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Before yesterday I would have said no or very little effect from a mag BUT Yesterday I was shooting my new 300blk at 100 yards off an Atlas Bipod legs down one notch so I would not rest on a mag base. Shooting 168 smk RL-7 handloads with a 20 rd Gen 2 Pmag I was getting severe verticle stringing, for the last 5 round group I used a C Products 30rd got a centered 1 1/2 group (that was the only change in 4 strings) The P Mag also would (2 different instances) strip a round out of the mag push it into the chamber but the bolt would not be snapped on the cartridge This Rifle shoots well with C Products, and when the rounds stay put with Lancer L5 but did not care for the Gen 2 P Mag at all Upon further review... I went to load another ladder from 17.7--18.1 and saw powder granuals in the bottom of the loading block EXCEPT for where the last 5 rounds were loaded from (it is a universal block, seems 300blk is TOO short to sit deep in the block and have the RCBS funnel fully seat) I would bet there will be NO stringing next range session. |
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upper/lower fit has no affect on accuracy. Quoted:
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Just a WAG, but is there any chance that the magazine could affect the fit of the upper and lower, and hence the accuracy? Don't beat me up for this; I'm just thinking out loud. Moon upper/lower fit has no affect on accuracy. I've heard that before, but intuitively it seems unlikely; a change in where the pressure is on the upper seems as if it should have some effect on where the bullet strikes. We won't revisit the 'accu-wedge' business, but there is a perceived problem on that issue. Moon |
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I've heard that before, but intuitively it seems unlikely; a change in where the pressure is on the upper seems as if it should have some effect on where the bullet strikes. We won't revisit the 'accu-wedge' business, but there is a perceived problem on that issue. Moon Quoted:
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Just a WAG, but is there any chance that the magazine could affect the fit of the upper and lower, and hence the accuracy? Don't beat me up for this; I'm just thinking out loud. Moon upper/lower fit has no affect on accuracy. I've heard that before, but intuitively it seems unlikely; a change in where the pressure is on the upper seems as if it should have some effect on where the bullet strikes. We won't revisit the 'accu-wedge' business, but there is a perceived problem on that issue. Moon Despite what "seems" or is "perceived" to be, the fact remains. No effect on accuracy. |
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Despite what "seems" or is "perceived" to be, the fact remains. No effect on accuracy. Quoted:
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Just a WAG, but is there any chance that the magazine could affect the fit of the upper and lower, and hence the accuracy? Don't beat me up for this; I'm just thinking out loud. Moon upper/lower fit has no affect on accuracy. I've heard that before, but intuitively it seems unlikely; a change in where the pressure is on the upper seems as if it should have some effect on where the bullet strikes. We won't revisit the 'accu-wedge' business, but there is a perceived problem on that issue. Moon Despite what "seems" or is "perceived" to be, the fact remains. No effect on accuracy. I'll have to agree. Unless the upper/lower fitment is so loose that the mere pull of the trigger causes said upper/lower combo to actually flop from one side to another before the hammer can strike the firing pin: then I see no effect on accuracy. Something that is that loose would be so evidently FUBAR you wouldn't even bother trying to shoot it in the first place... |
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I'll have to agree. Unless the upper/lower fitment is so loose that the mere pull of the trigger causes said upper/lower combo to actually flop from one side to another before the hammer can strike the firing pin: then I see no effect on accuracy. Something that is that loose would be so evidently FUBAR you wouldn't even bother trying to shoot it in the first place... Quoted:
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Just a WAG, but is there any chance that the magazine could affect the fit of the upper and lower, and hence the accuracy? Don't beat me up for this; I'm just thinking out loud. Moon upper/lower fit has no affect on accuracy. I've heard that before, but intuitively it seems unlikely; a change in where the pressure is on the upper seems as if it should have some effect on where the bullet strikes. We won't revisit the 'accu-wedge' business, but there is a perceived problem on that issue. Moon Despite what "seems" or is "perceived" to be, the fact remains. No effect on accuracy. I'll have to agree. Unless the upper/lower fitment is so loose that the mere pull of the trigger causes said upper/lower combo to actually flop from one side to another before the hammer can strike the firing pin: then I see no effect on accuracy. Something that is that loose would be so evidently FUBAR you wouldn't even bother trying to shoot it in the first place... I think that would be very dangerous to have a upper/lower that is fitted loosely. I would imagine the bolt going back would possibly injure you or others or even destroy the weapon depending on how it files back. |
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Is he using the mag as a rest? My USGI mags have a lot more wobble than my Pmags. Quoted:
Is he using the mag as a rest? My USGI mags have a lot more wobble than my Pmags. Quoted:
Unless you're using the mag as a rest/monpod or the mag is damaging (i.e. scratching/scoring the round or causing it to hit the lugs in the barrel extensions in such a way as to damage or dent/bend the round) then there is no other way it can affect accuracy. I have to agree with these two. It sounds to me like he's using the mag as a rest or somehow holding it. Another crazy guess here is that the magazine is being loaded with all 30 rounds and thereby creating increased pressure on the bolt. When the first round is fired, the bolt has to work "that much harder" to travel back. My advice is to do an experiment. Load all rounds, test it. Then load less 2 rounds and see if that changes. |
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I think that would be very dangerous to have a upper/lower that is fitted loosely. I would imagine the bolt going back would possibly injure you or others or even destroy the weapon depending on how it files back. I have never seen or heard of an upper/lower fit that was anywhere near that loose, and I'd venture to guess that neither have you. Let's stick to actual possibilities here. |
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I would believe this could lead to feeding issues and not accuracy problems unless the round is getting severely scratched/gouged upon entering the chamber. Quoted:
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Is he using the mag as a rest? My USGI mags have a lot more wobble than my Pmags. I would believe this could lead to feeding issues and not accuracy problems unless the round is getting severely scratched/gouged upon entering the chamber. I was implying that he is not resetting back to the same point. So after each shot his is in a slightly different shooting position. |
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