AR Sponsor
Posted: 5/28/2007 11:38:44 AM EDT
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Well after handling many armory M16's in the Marine Corps to owing a dozen of my own AR's I finally have met my match and I need help. I have a new LMT upper that came with out a bolt carrier group. I then bought, from a store a new LMT bolt carrier group.So I thought I would have zero problems. Yeah right. I am not knocking LMT yet. I just need to find the source of the problem and fix it so I can shoot! Here we go: My bolt lugs will not enter my chamber lugs 100% of the time. Maybe 3 or 4 out of 10 tries fails. My bolt will not unlock and be allowed to be pulled to the rear the same number of tries 3 or 4 out of 10 tries fails. When unlocking the bolt lugs from the chamber lugs it withdraws to the point of the lugs being all in line and trying to pass each other. So in other words there are no missing spaces between each lug each space is filled with a lug and in the ejection port you can see all of the bolt shaft sticking out of the front of the bolt carrier group. I have done this on a completely assembled rifle at the range with live rounds and done it at home with the firing pin removed and on or off the lower. I have tried to cycle it with rounds and with out. It makes no difference! Same problem. I have taken the upper a part and torqued to 30 and to 80 and in between. Same thing. I have lubed the lugs and entire bolt carrier with more lube than I would ever fire it with it's sloppy wet right now. I have looked for burs on both sets of lugs but I can't see any with the eye. Do I need to be looking with a magnifying glass? Wouldn't such a tiny burr be insignificant? It also did not fire the 2 different times I have taken it to the range. I have inserted spent brass and dropped the hammer but can't tell if I get hit on the spent primer or not. I do not get light hits at all on live rounds. I get nothing. When I do get 100% lug lock up I have to use something to lightly beat/tap open the charging handle (which luckily is not bent yet!). What the hell is wrong with my upper guys? Anyone? ****** edited to add a new observation I removed the bolt from the bolt carrier to work the bolt by hand in and out of the chamber lugs. There was absolutely no problem, no drag moving the lugs in and out of each other. So I think the problem is now the bolt carrier must be out of spec and has the bolt on an angle when moving in and out of the lugs maybe??? |
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Ok I sorted it out with process of elimination. The bolt had no issues at all. The chamber lugs had no issue at all. The bolt carrier had some type of burr or "finish" build up in the wrong area internally. So after trying to pinpoint where the problem area was with countless racking of the bolt and it getting stuck, my unsticking it, then racking for more of the same. It polished itself in and now it locks and unlocks. I fired a couple a primed pieces of brass too! So it now fires also. I do notice it is hard to unlock and extract the primed brass but that is probably becuase of case expansion with out enough energy to extract so I doubt this will be a problem with live rounds. Well I hope this helps somebody, one day when they are pulling their hair out! |
Did you check the back section of the bolt to see if there was a bulged/higher section of steel just before the bugle section? Every once in a will, the milling machine can dance a bit, and the last 1/4" of straight round section is a bit larger than the rest of the shaft, and higher section can bind up in the back carriers gas section channel for the bolt to pass out the back. |
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