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Posted: 5/18/2002 8:43:46 PM EDT
Hi everyone, I'm having a strange type of jamming problem on my Bushmaster 16" AR-15 (actaully XM15-E2S).

Once every 30 rounds or so, at any point in any magazine, the bolt seems to only strip the round half way off the mag and doesn't go all the way "home." The weird part is that if I shake the rifle just a little bit, sometimes the bolt picks up again and finishes going forward. IT's like it's just barely catching on something, and I can't figure out what it is.

It may be important to note that this problem started occuring recently after installing both a JP single stage trigger and Ti firing pin. Could these parts be the culprits? Thanks for any help.

P.S. When the bolt does continue forward after shaking or tapping the gun, the hammer is still cocked back and ready to fire, so I don't think that the hammer is following, although, like I said, I'm not sure what the problem is.
Link Posted: 5/18/2002 9:19:34 PM EDT
What type of magazine are you using? Have you tried it with a different mag to see how it works? If you are using a cheap mag like a USA, that may be your problem. Try using a G.I. issue mag and see if that helps.

If it still does this, then you may have an out of spec part of something may be loose/not properly installed. Check everything out and see if you see any problems.
Link Posted: 5/18/2002 9:29:39 PM EDT
probably the magazines. Ive always been amazed that given the popularity of the ar15 rifle, noone has ever manufactured a decent quality magazine for them. If it wasnt for the stupid hicap ban id start manufacturing high quality steel mags, with a follower designed similar to the ak47 follower.
Link Posted: 5/18/2002 11:52:01 PM EDT
Unfortunately, it's definately not the magazines. All of my magazines are USGI 30 rounders, some are even factory colt marked.

I'm thinking it might have something to do with the JP "speed hammer" binding the bolt carrier up somehow on the forward motion... which is where the thing stops, same place (about 3/4 the way forward) every time.

The really weird thing about this jam is that you can literally fix it by shaking the rifle around... sometimes it even fixes itself it you let it sit for a couple of seconds. It's like the bolt, bolt carrier, or something similar is getting caught up on some other part, I just can't figure out what it might be. Tomorrow I'm going to go to the range with a few hundred rounds and try to figure it out. I'm guessing is probably has something to do with my new trigger/hammer setup, I just can't figure out how a trigger group could cause such a malfunction. Anyway, thanks for the suggestions so far, your help is much appreciated.

Link Posted: 5/19/2002 12:43:11 AM EDT
I wish I had more mechanical smarts about the AR....unfortunately if something gets wrong I just tinker with it until I make it right again. Troy will probably have the answer for you whenever he comes across this thread. Sorry I couldn't help more.
Link Posted: 5/19/2002 12:59:46 AM EDT
mine does this occasionally as well, strangly enough only with my only two GI 30 round magazines, with green followers (my rifle also has an occasional jam with these as well).  I have two 30 round Thermolds that function flawlessly in my Bushmaster.  
Link Posted: 5/19/2002 1:00:49 AM EDT
This is going to sound pretty nuts, but I've come up with a "theory."

I was looking at my rifle's guts and noted some wear in areas that I did not expect. There is a lot of wear on the top of the notch of the hammer as well as on the back of the firing pin (not the striking face, but the surrounding area).

I have noticed that this problem occurs more frequently when I use this cyclic rate reducing pneumatic buffer that I have.

The problem does not seem to occur when I make an effort to hold the trigger down firmly throughout the entire firing cycle; if I release the trigger before the next round goes into battery, then the problem may arise. This makes me think that having the hammer held back by the disconnector prevents this jam.

So here's my theory: the notch on the hammer is somehow catching on something, most likely the firing pin, on the forward stroke of the bolt carrier. However, the hammer lies to low to catch on whatever it is it's catching on unless it has been released from the disconnector (which allows it to rise up a bit. I have noted that my titanium firing pin has a larger flange on it than the original steel firing pin that came with my bushmaster. Perhaps this enlarged flange is contributing to the problem?

Additionally, the jam position corresponds to the part of the cycle where the hammer is beginning to ride up that ramp on the bolt carrier, right where the firing pin is.


Has anyone ever seen anything like this before? Does this make any sense? Thanks for all the help so far.
Link Posted: 5/19/2002 3:27:49 AM EDT
[Last Edit: 5/19/2002 9:26:58 AM EDT by raf]
Link Posted: 5/19/2002 4:38:30 AM EDT
[Last Edit: 5/19/2002 4:45:54 AM EDT by tatjana]

Originally Posted By blackrazor:
Unfortunately, it's definately not the magazines. All of my magazines are USGI 30 rounders, some are even factory colt marked.

I'm thinking it might have something to do with the JP "speed hammer" binding the bolt carrier up somehow on the forward motion... which is where the thing stops, same place (about 3/4 the way forward) every time.



Dump the "speed hammer."  It just causes more problems than it's worth.  It also doesn't really do much for "lock time" which is the marketing spin they put on its value.

As for buffer springs and such... I prefer the bolt groups in my rifles in general to be stiff and heavy.  That bolt shouldn't even think about hanging up.  Too many opportunities to fail for small things that a nice potent bolt would plow through without fail.

Personally, I'd dump your Titanium firing pin too.  I've never been a fan of those.  I'm not alone in my aloof attitude towards them either.  Consider Aramlite's view of them:


October 12, 1997

TECHNICAL NOTE 2: TITANIUM FIRING PINS ARMALITE CONSIDERS GENERALLY USELESS



www.armalite.com/library/techNotes/tnote02.htm

As for your malfunction, sounds like you might have a grip on it.  Perhaps the speed hammer is TOO fast...?

As for trigger technique, it sounds like your jerking it a bit if you actually are coming off the trigger before the next round comes into battery.  That's unlikely to give you the nice, smooth trigger motion that you should strive for.  You should be squeezing through that trigger all the way to it's stop- following through as it were- and then easing off just until the "click" and "click-resetting" the trigger on every shot (provided your JP single stage actually permits such function- which it should). "BOOM!  SPROING! (short pause) -click-" (Oh my, I do so love that sound).  Lather, rinse, repeat.
Link Posted: 5/19/2002 9:00:20 PM EDT
Fixed it! But you'll never guess what the problem was. I went back to the range today and observed the jam more closely... the bolt kept stopping at the exact same point, but ONLY when a round from the left side of a magazine was being stripped off. So it turns out the jam was caused by some burr on the left side feed ramp. Fixed it up pretty quick with one of my spyderco knife sharpener stones.

Tatanja... you mention that you like your rifles to have a heavy spring, and I must admit that is seems this may never have been a problem if my recoil spring had more power. Do you know where you can get a higher power (more force) recoil spring for the AR rifle? Thanks.
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