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Posted: 1/22/2004 9:32:04 AM EDT
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Ok heres the problem, but first a little background. I rencently swapped my 16" JT kit barrel and upper for a flat top upper from model 1 with a 14" M4 barrel from bushmaster. Now my problem, when I fired the very first round yesterday out of this gun it jammed. The spent case got stuck between the bolt face, and the front of the charging handle...which meant I couldnt pull the charging handle back, I was able to get the stuck shell out with a screw driver...but then I kept getting more and more jams...it was like it would kick the spent case out, and try to feed the next round in too soon. so I had a jam with a spent case and new round stuck in the locking lugs. had to drop the mag and work the charging handle. This was done with S. african 5.56 ammo. then for the odd part, when I switched mags to ones loaded with the new polycoated wolf, it would fire almost perfect...although I would still get the same jam with one spent case and one new round and would have to do the drop mag and work charging handle routine. Now Im wondering WHY would it work with the cheap wolf ammo better then the SA stuff? before I switched barrels it functioned flawlessly. Now for some more background info...I think the problem could be the gas tube as I reused my old one...however when i was attempting to remove it from my old barrel I had quite the bitch of a time getting it out, so It got chewed up quite a bit from locking pliers...I think I maybe even dented it a little. so im wondering if this problem could be the gas tube? I have ordered one because I should replace it anyways. but any help on this would be greatly appreciated. -Brian- |
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Sounds like it is short stroking. If you load one round in a mag, charge and fire, does the bolt lock back? If not, it is short stroking for sure. If the gas tube is badly dented, attend to that first so as to eliminate excess possibilities. Also, only change one thing at a time, then function test, otherwise you may miss the real problem. I think there is a FAQ on short stroking, might be worth looking at the stickies at the top. |
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Quoted: If the gas tube is badly dented, attend to that first so as to eliminate excess possibilities. Also, only change one thing at a time, then function test, otherwise you may miss the real problem. From your description, the above sounds like good advise. Change out the gas tube first. |
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ya I plan to change the tube (ordered one last night) as for locking back the bolt, It did most of the time...thats what was so weird about this problem, it seemed like it would only short stroke some of the time. And the weirdest of them is it worked the best with the Wolf ammo then it did with my S. african...going by the fact that it was operating better with the crap ammo then the good stuff, id be even more affraid to try my XM193 in it...lol, j/k thanks for the info guys...I hope the gas tube fixes this prob. -Brian- |
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Sounds like you might have a weak ejector/extractor too, since the case is staying partway in the gun. Have you checked that the carrier key screws are tight? Did you mic the end (bolt carrier end) of the gas tube to check for wear before you re installed it? First check is for short strokes tho. |
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Is the gas tube roll pin present? The 14.5" barrels (uh, is it 16" OAL, or did you NFA it?) run harder than the 16" barrels and need stiffer extractors. The jam you experience between the bolt face and the charging handle is usually related to a weak extactor. The extractor bounces loose at the end of the battery stroke. If it's weak it will release the case completely. Also, when you changed the barrel you may have altered the HS. Tight HS will cause FtEx, FtEj, and SS too. Quit testing with the Wolf and use the XM193, you'll save a lot of tail chasing. Go to the range. Load one known good round in several known good magazines, load each mag into the rifle and fire the rifle while holding it as loosely as possible (one handed, butt not touching your shoulder). The bolt should lock back. If it doesn't lock back after several tries repeat but this time press in on the bolt catch and hold it when you fire. The bolt should lock back every time. The reason for pressing in on the bolt catch is to weed out a bad mag or bad bolt catch. Make sure that the face of the bolt is behind the bolt catch. Sometimes a bolt will lock open but it's the carrier that is caught on the bolt catch and not the face of the bolt. If the rifle locks open it's not shortstroking. Much more info about short stroking than I feel like re typing in[url=http://ar15.com/forums/announcement.html?b=3&f=66&id=185]FAQ II[/url]. Speaking of which, does your BFI "M4" barrel have the M4 feed ramps? If so, does the Model 1 upper have the corresponding correct ones in it? If all that is gibberish to you, read [url=http://ar15.com/forums/announcement.html?b=3&f=66&id=186]FAQ I[/url] If you're in N OR SMP, my days are pretty free now. Always happy to help an ARFer. |
| I had a very similar problem with a new 16" BMI upper I put on an older BMI lower. The expended case would end up jammed up into the lugs or charging handle never fully clearing the chamber on it's way out. It was falling off the extractor as it was pulled from the breech. A new heavy duty extractor spring (with the black insert) cured it completely. |
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Tweak: Im right near the portland area...as for the barrel it is the 14 1/2" one, with a KKF A3 Tac brake installed. As for the M4 cut feed ramps, I dont think they are...at least they dont look like the ones that where in the pic in the FAQ 1. I didnt realize the 14 1/2 barrels where harder to run, I guess it could also be the extractor spring then. where could I find the heavy duty ones mentioned? thanks again to everyone whose trying to help me figure this out, I've said it b4 and I'll say it again...AR15.com is the reason I have no money, but they never let me down! -Brian- |
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So the barrel is Fed legal then, 16" OAL as I'm assuming the KKF brake is perm attached. Just checking, you wouldn't believe some of the Qs that get asked here. [:)] One of the best places for parts is [url=http://sawlesales.com]Specialized Armament[/url] but he's got a minimum order IIRC. [url=http://www.brownells.com/Index.html]Brownells[/url] is always a good choice. Do you also have dedicated chamber brushes? |
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I just ordered the extra power extractor spring, and something called a D-axtractor...looks like a D shaped O-ring, its supposed to make it stronger too, so I figured I'd give it a try....I also ordered some headspace guages and The USGI cleaning kit which does have a chamber brush, which I needed too anyways. Im hoping this will cure the extraction probs...I also figured I should headspace it too see if the chamber may be too tight. Bushmaster says there barrels are allready factory headspaced so I figure it should be good, but since I plan to build a cheap 20" rifle soon I figure I better get the gauges anyway. I guess I'll see in a week or so if the problem is now fixed...thanks again for all the help. -brian- |
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