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Posted: 3/31/2003 2:59:00 PM EDT
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Ok, go grab a beer and come back to the computer, because this will be a long one. I built/had built a M4gery with the following parts: PWA lower with custom trigger job BM M4 fixed telestock with full buffer and spring DPMS flattop BM 1:9 HBAR 16" with Cav Arms brake USGI mags (20s and 30s) Bolt was headspaced just fine First day at the range was with 3 types of ammo: Winchester USA 55gr FMJ (the stuff you buy at Wally-world)--80 rounds Israeli? M855 greentip '93 headstamp--30 rounds Winchester USA 62gr FMJ--20 rounds Mags: 1 Colt 30rd mag (reloaded several times) 1 Parsons 20rd mag (reloaded once) 2 Parsons 30rd mag (one had the greentip, the other had the 62gr FMJ) I had thoroughly cleaned the rifle prior to the range, using Shooters Choice Bore Solvent on the barrel and chamber, and the lubed everything up with CLP. One thing I noticed, is when the bolt and bolt carrier were fully assembled, if I slung the bolt carrier, like some sling a bottle of ketchup, with the bolt retracted, centrifigal force wouldn't extend the bolt, no matter how much CLP was used. I figured because the upper hadn't been fired, it was just tight. The 55gr Win I shot first, from the Colt mag, and seemed to have many malfunctions, some of which were failure to extract (perhaps 10 times), failure to feed (bolt over the mag...no chambered round twice), and doubling (4 or 5 times) over the course of shooting the 55 gr. I tried the 20rd, and still had the same problems, but to a lesser degree. Most of the times the first round would fire (chambered from having the bolt back, then manipulating the bolt catch with magazine...did not need forward assist), but would then cause a stoppage. After I shot out all the 55 gr Winchester, I fired the greentip 30rd mag next. It was not the same mag as before, and had one stoppage (FTE). Last was 20 rounds of 62 gr Winchester, out of another 30 round mag, and everything was fine. Total round count: 130. That night I cleaned everything thoroughly, and applied CLP. I did replace the fixed telestock with the A2 buttstock and buffer that the lower came with originally. I replaced the Colt mag's follower and spring with a new green follower and new spring. I didn't do anything else. Saturday I went to shoot again. I used Q3131A from Midway, collected some more magazines (including the repaired Colt), and went shooting. I had 60 rounds of 62gr Winchester left over, in two other mags, as well as 5 boxes of Q3131A loaded in two 20s (one was from the previous time), as well as rounds loaded in the other 30rd magazines, including 20 rounds loaded in the Colt mag. After no malfunctions for the rest of the 62gr, as well as perhaps 40 more rounds of Q3131A, I loaded the Colt mag, and sent the bolt forward. I fired one round. As I noticed that something wasn't right, I ejected the magazine, and inspected the chamber, only to find the bolt and carrier only 2 or 3 inches out of battery with the spent case (ass first) stuck between the top of the bolt locking lugs and the charging handle/top of the receiver, and the front hanging down. That case was completely wedged in there, and I couldn't move the bolt at all. The only way I figured out to remove the case was to remove the buttstock, buffer, buffer detent and spring, and then pull the bolt out the back of the rifle. No odd marks were on the casing (just some scratches from the lugs and the extractor). Nothing looked damaged or out of place, so I reassembled the rifle, and shot the remainder of my ammunition, but not from that Colt mag. I figured in the beginning my rifle had problems because it was: tight and new, shooting crappy Winchester 55 gr (NOT Q3131A), and perhaps a bad mag (the Colt). However, even with the new follower and spring, better ammo, and being broken in a little, the rifle still had a stoppage. I attribute this problem to the Colt mag, but am checking in here just to double check. I compared the mag with others that I know work, and can't see any physical difference. I'll take pictures of whatever if it will help. Total rounds is now at 290. Thanks in advance for the help, -Zmeja |
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Quoted: However, even with the new follower and spring, better ammo, and being broken in a little, the rifle still had a stoppage. I attribute this problem to the Colt mag, but am checking in here just to double check. I compared the mag with others that I know work, and can't see any physical difference. I'll take pictures of whatever if it will help. -Zmeja You don't need to post photos; the problem is an easy fix. Here is the problem with the mag. When loaded, the middle of the mag at the feed lips is bowed out. When the bolt passes over the top round, the increased staggered angle/offset of the rounds in the mag causes the top round to be jammed against the side of the mag, in between the feed lip and the top of the indent rib, instead of the top round just being pushed down. This cause the carrier to bind, and causes all kinds of problems. It's a staggered geometry equation with related stress forces to achieve downward force of the offset cylindrical objects with relationship to the containment walls structural strength. To fix the mag, pull the spring and follower out of the mag, and squeeze the middle of the mag together just at the end of the feed lip to tweak the middle slightly inward. When the mag is loaded, the middle walls/feed lips will be straight with the front/back of the mag, and when the carrier comes back, over the top round, the top round will be pushed down, without the top round being wedged and binding the carrier. Or you can just chuck the mag and replace it with a new one that is not flexing at the middle. |
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Dano, Thanks for the help. I got the mag from a friend who knew I was into rifles and thought I may have wanted it. The mag itself has a rather worn finish looking like it was brass colored too. I know that finish doesn't necessarily make or break a magazine's performance, so that is why I took it. I'm just glad I didn't pay for it. I need to get new magazines anyway...after all, I only have 9 30 rounders! -Zmeja |
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You may want to check the mag at the back of the lips/U channel for the bolt catch lever. If the lips are cracked, the tweak will work, but just use the mag for you range work. Sooner or later the cracks will open up the feed lips angle and the mag will double feed/ spray rounds into the upper receiver. Fun to watch, bu not when it happens to your own rifle. |
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