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Posted: 4/17/2006 7:01:31 AM EDT
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Buddy of mine has Bushmaster Modular Carbine which has around 1100 rounds thorough has some really odd failures to feed. Most of the shots has been different testing in various configurations... Problems started to occur after carbine was shot around 400- 500 hundreds rounds(and after I threaded his barrel for muzzle brake). First rifle cycles normally but sometimes it simply won´t feed from left side of the magazine and this could happen anywhere between shots 1 - 30. Rifle came with 5 new D&H 30 round mags and all of them have same FTF. When you look through ejection port you can see bullet stuck on left feedramp on barrel extension. When charging handle is racked slightly or bottom of the magazine is slapped gently bolt goes forward and slams home without a problem. First thing came to my mind was gas problems and loose gas key but key is ok and screws are tight so no problem here. Then I checked the bolt for cracks, also no problems. Next on check list was receiver extension and buffer. Buffer bumper pin was in place and foreign matter in tube. Then we tried brand new D&H mags which work on all of my rifles, same FTF, left side of magazine again. At this point I got really confused, I didn´t have no damn idea what might cause this and we decided to test couple of my telestocked lowers with 5.54 oz and 5.65 oz buffers. Rifle worked fine for couple of mags but it was just lubed and cleaned very well. I even tried Randall Rausch tip to shoot rifle without support to stock, BC locks back with heavy steel buffer so there isn´t possibly any gas problems. Then problems started again with both telestock lowers...  and yes, again left side of the mag.Next thing was to change M16 carrier with his bolt (cleaned and lubed), no help. Rest of the check list: Gas block off to check gas port alignment, ok. Gas tube, no obsructions. Gas tube hole alignment between upper and barrel nut, ok. Gas key hole, no obstructions. Gas rings, condition ok. Mag release tightening by one whole revolution. There also isn´t any signs of gas leaks more than normal compared to other ARs. Needless to say, I´m pretty desperate... Just when you thought you know something about AR´s, you realize you don´t know shit about them... So, if anyone could give me some info I´d really appreciate. Thank you, MN ETA: Ammo used with this rifle is American Eagle 55gr FMJ loaded to Lake City 04 cases, no Wolf or other crap, so this won´t be ammunition related. |
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Pull the mags apart, and stone down the bottom of the feed lip edges to remove the sharp stamp bur’g edge on the bottom of the lips. From there, take a good look at the index of the barrel extension in the upper. The middle point of the two feed ramps should be dead center bottom of the upper receiver bottom. |
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I am having the very same trouble and am just as perplexed. My rifle is a Bushmaster Dissapator model. It worked flawlessly using xm193 and win white box for ~2000 rounds. I changed from the A2 stock to collapsable at around 1000 rounds, and had no trouble until the last 200 rounds or so. The last 3 times I went to the range, I had the same symptoms: first 2 mags ran fine, then the FTF's started. Sometimes a complete failure to feed, sometimes the bolt would hang on a round (stuck on feed ramp). If I slap the mag or pull charging handle, the bolt goes into battery. I have checked gas ring alignment, magazines, gas key, gas tube wear, etc. I have observed the exact same problem with other magazines as well as my own. I have carefully observed the bolt interacing with the round and the magazine feed lps, and I cannot see any contact between bolt lugs and feed lips. All looks good. What to do? -Turbok |
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If the round is getting stuck on the feed lip, either the bolt is having a hard time stripping the round out of the mag, or the hammer is catching the FP collar and slowing down the stripping stroke. To weed out the problems, do check to make sure that the bolt is locking back on the last fired round out of the mag (read you do have correct cycle/function to begin with). |
Fits in a picture if old style BC is used but my buddys rifle is with new Enhanced BC. I´m leaning pretty strongly on gas problems. After telephone conversation owner of the rifle told there is huge wobble between gas tube and gas block. After next range trip we will see... MN |
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