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Posted: 4/7/2017 6:31:22 PM EDT
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Just got finished with an AR10 build. Having an odd issue I can't figure out. If I drop the mag and load a round at a time .62 is my grouping. When I load a mag it's closer to 4.5in. If the round is left side of the mag I miss left, right side miss will be right. I have tried several different mag types same result.
First thought is mag is putting pressure on the carrier? Would this miss left or right ? Or low? Second thought it's a carrier issue? Considering ordering an another carrier maybe even bolt as well? Any thoughts? |
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Allow the rig to strip the second round normally from the magazine, but don't fire it...
Remove the round from the chamber very slowly and carefully. You have two choices, you can repeat this and collect about 5 or ten samples of these and fire them to see if they are so damaged that the group opens when compared to single feed. or... You could just collect about three to five and inspect them for damage. If you don't really find them damaged, or if firing them single feed takes you back to a good group, then you will need to check the dimensions of the BCG, BBL extension, and Upper, etc. inspected. If you have any friends or spare BCG parts handy, a swap there might answer some questions too. Step one is to check the COAL and TIR. Good Luck |
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Take a few rounds, and measure the OAL of each, and write it down. Now load them in the magazine, and chamber them by pulling back the charging handle and letting it fly home. Measure the OAL of each after.
I did that on my AR15 some years back, and was surprised at the results - not just how much the bullets moved during chambering, but that some would move forward, some would move back. Depending on your bullet, how close they are to the lands, etc., having them move could mean a significant accuracy difference. Going to 4.5 inches is much more than I would expect, but it's still worth investigating. |
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I seated a magazine, chambered a round and removed it. Repeated this 7 times.
Noticed a small scratch/not really a gouge ion the projectile. A very close inspection of the barrel revealed a small burr, on the feed ramp. When fired one at a time, group was as tight as before. Swapped BCG's used a magazine, grouping was very tight. So looks as if the mystery has been solved. Any issues with having the burr polished out? |
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