I have a Bushmaster that has a very consistent failure to extract.  It's typically one to two rounds for every one hundred fired.  I've had two gunsmiths fail to figure out the problem.

By the way, I know you won't need all of this info but I'll give it to you anyway.

Ammo type has varied, but it'll do it about the same with any kind of ammo I've tried.  I typically shoot Black Hills 55 grn. FMJ or 68 grn. Heavy Match HPs or Winchester white box.   Magazines are new Colt 30-rounders, no apparent difference with any mags used.

About the rifle: It's all Bushmaster, with a 14.5'' barrel with permanently mounted Phantom supressor to get it to a legal length.  It has a standard full length stock and Bushy flattop upper.  Gunsmiths have checked the gas tube and found it to be straight and clean.  I have a lot of extra parts so I've tried swapping out extractor claws and springs.  No change.  I've also replaced the buffer spring with another standard spring, no change.  None of them appeared damaged or non-standard in the first place, but I figured I had the parts so I may as well try.  I keep the rifle very clean and in fact have had the gunsmiths comment on how well maintained it appears.  I oil it as per the Bushmaster owners manual.

The jam itself:    Yesterday, as an example, 100 rounds fired.  Jammed on about the 6th shot, then three times throughout the rest of the shooting.  Does not seem to matter if the gun is hot or cold.  The spent casing is pulled back partially and then left with about two thirds of the casing exposed.  I failed to check the shell casings yesterday for claw marks but have not typically seen any deformation or cuts from the extractor on the casing.  The bolt appears to be moving all the way to the rear and then coming back forward strongly as the next round is always driven hard into the bottom of the spent case still partially in the chamber.  Usually by dropping the magazine I can cause them all to fall out but if the spent casing is still only a third of the way out or so I'll have to use a pocket knife to pop it out of the chamber.  One of the four jams yesterday required this.

Please help!  This problem has been consistent for over two years with this gun.  I've wondered if it has something to do with the shorter barrel.  I've had it checked by gunsmiths on two occasions and sent back to Bushmaster once.  The local gunsmiths couldn't figure anything out at all that appeared wrong, Bushmaster was able to reduce the number of jams but not stop it.

I'll be checking into the thread frequently, so ask any questions you want!

Thanks, guys!

Quoted: The spent casing is pulled back partially and then left with about two thirds of the casing exposed...The bolt appears to be moving all the way to the rear and then coming back forward strongly as the next round is always driven hard into the bottom of the spent case still partially in the chamber.

It still sounds like you have a weak extractor spring (even though you've swapped it out), as the extractor is slipping off before extraction is completed. Pick up a Wolff HD extractor spring, and chances are it will cure your problem.

How does your chamber look?

Does the bolt lock all the way back on the last round?  Consistantly?  I would inspect the chamber for obvious burrs, then I would make sure the bolt is locking back on the last round of every mag to make sure it's not short stroking and then I would replace the extractor spring with a Colt HD or a Wolff extra power spring.

Well, from what I can tell the chamber looks fine.  I've used a Surefire to light it up well, but never been able to observe any scratches in there.  Of course, I've never taken the barrel off so I can't see one side of the chamber.  But what I can see looks smooth.

Also, I have not noticed the bolt failing to lock back after the last round.  I will experiment some and pay attention to that, but I haven't seen it do that since it came back from Bushmaster.  It did indeed used to do that, but I believe that problem was solved.
ETA: I am going to try to take it out tonight and pay attention to that.  Also, where can I buy the Wolff Heavy Duty springs?  I'm googling it but having a hard time telling if what I'm finding is what I need!

Quoted: Also, where can I buy the Wolff Heavy Duty springs?

www.gunsprings.com/RifleShotgun/Colt_RsNF.html#M4Ext

Don't worry about the black insert that they recommend you use with it. Just use whatever color you already own and you will be fine.

Wow, thanks for the quick reply.

I'm kind of embarrassed to not know for sure about the bolt locking back.  I suppose if that's the case then it's short stroking, which I really hope it's not!  I've always been kind of worried that might be it with a shorter than normal barrel.

Quoted: Also, I have not noticed the bolt failing to lock back after the last round.  I will experiment some and pay attention to that, but I haven't seen it do that since it came back from Bushmaster.  It did indeed used to do that, but I believe that problem was solved. ETA: I am going to try to take it out tonight and pay attention to that.  Also, where can I buy the Wolff Heavy Duty springs?  I'm googling it but having a hard time telling if what I'm finding is what I need!

Double check the gas key just to be sure.  

I have checked the gas key.  It still seems to be staked down solidly.

Have you made sure the gas rings do not have the slots lined up?

Yeah, I'm always real careful about the rings not being lined up when I clean it.

Quoted: Have you made sure the gas rings do not have the slots lined up?

That's an old wives' tale. If aligned gas ring gaps cause your rifle to malfunction, you've got more serious problems.

OK, guys...

I took the rifle out yesterday evening along with another AR that works perfectly to do some testing.

First I placed 1, 2, or 3 rounds in a mag and fired normally.  The rifle always locked back and ejected, with the exception of one time when it locked back and the shell casing was floating inside, totally clear from both the bolt and chamber but had not been kicked out.  So that got me kind of confused, but I began thinking it was indeed an extractor problem.

Then I tried holding the gun a little looser and doing the exact same thing.  The gun immediately started failing to lock back on almost every last round and would fail to eject on about one out of every three rounds.  If there was another round in the magazine I would get the exact jam that I have been getting, with the spent casing partially in the chamber and the next live round wedged in hard underneath it.  This was very consistent and repeatable- with a loose grip on the gun, it WILL fail to lock back, guaranteed, and will very likely fail to eject.

We then attempted me holding my friend's functioning AR in the exact same loose way that caused mine to fail, and his functioned perfectly.  Just to further identify problems, I removed the bolt and carrier from mine and replaced it with his.  My AR failed to lock back when fired loosely with his bolt/carrier group and in fact seemed to fail to eject the spent casing even more often than with my own bolt/carrier.  So, if anything, my bolt worked better.  His gun, meanwhile, still functioned perfectly even when held loosely with my bolt/carrier in it.  So the problem does not seem to be in the bolt/carrier group.

So there you have it.  It seems my gun is right on the edge of having a workable ammount of gas.  If it's held tightly and none of its' gas is wasted, it'll function right MOST of the time and I'll only get the jam that I've described every one in one hundred rounds or so.  But if the gun is held even the slightest bit loosely and any of the pressure of the gas is wasted moving the weapon then it WILL fail.  And since I was shooting at longer than normal ranges on Saturday at the competition I was holding it loosely to try to avoid jiggling it and thus guaranteed a massive number of jams.

So, now how do I fix it?

Quoted: OK, guys... I took the rifle out yesterday evening along with another AR that works perfectly to do some testing. First I placed 1, 2, or 3 rounds in a mag and fired normally.  The rifle always locked back and ejected, with the exception of one time when it locked back and the shell casing was floating inside, totally clear from both the bolt and chamber but had not been kicked out.  So that got me kind of confused, but I began thinking it was indeed an extractor problem. Sounds like an extractor problem Then I tried holding the gun a little looser and doing the exact same thing.  The gun immediately started failing to lock back on almost every last round and would fail to eject on about one out of every three rounds.  If there was another round in the magazine I would get the exact jam that I have been getting, with the spent casing partially in the chamber and the next live round wedged in hard underneath it.  This was very consistent and repeatable- with a loose grip on the gun, it WILL fail to lock back, guaranteed, and will very likely fail to eject. We then attempted me holding my friend's functioning AR in the exact same loose way that caused mine to fail, and his functioned perfectly.  Just to further identify problems, I removed the bolt and carrier from mine and replaced it with his.  My AR failed to lock back when fired loosely with his bolt/carrier group and in fact seemed to fail to eject the spent casing even more often than with my own bolt/carrier.  So, if anything, my bolt worked better.  His gun, meanwhile, still functioned perfectly even when held loosely with my bolt/carrier in it.  So the problem does not seem to be in the bolt/carrier group. So there you have it.  It seems my gun is right on the edge of having a workable ammount of gas.  If it's held tightly and none of its' gas is wasted, it'll function right MOST of the time and I'll only get the jam that I've described every one in one hundred rounds or so.  But if the gun is held even the slightest bit loosely and any of the pressure of the gas is wasted moving the weapon then it WILL fail.  And since I was shooting at longer than normal ranges on Saturday at the competition I was holding it loosely to try to avoid jiggling it and thus guaranteed a massive number of jams. So, now how do I fix it?

This may be a long shot but make sure the gas tube roll pin is not missing from the FSB.  In addition, if you have the means to remove the gas tube do so and ensure that it is not installed upside down.

So you still think there may be an extractor problem on top of the short stroke as well?

I don't think it's an extractor problem. I put my bolt and bolt carrier into his gun. It actually made it short stroke even more. I have had ZERO reliability issues with my weapon, besides a charging handle that was out of spec. If it was an extractor problem, or a problem with the bolt carrier assembly in any way it should have been fixed when we put my carrier assembly in his gun as it's already been proven to function reliably.

We were able to consistantly recreate the short stroke. All you had to do was hold his weapon loosly, like you were going to bumpfire, and it would short stroke. Often it would pull the casing back, not eject it,  then chamber the empty casing again. However, if you held his rifle up tight against the shoulder, it would function the way it was supposed to even locking open at the last round. We would do three short strokes, one round at a time, by holding it loose, then we would fire three more rounds of the same ammunition reliably by holding the rifle tighter.

I figure that it's a gas problem of some sort and that it's right at the threshhold of enough gas pressure to operate the action so long as the gun is firmly planted.

This is why I still think there might be some sort of extraction issue:

with the exception of one time when it locked back and the shell casing was floating inside, totally clear from both the bolt and chamber but had not been kicked out.

That sounds like a classic weak extractor spring issue...the extractor can't hold onto the case long enough for the ejector to do it's job.

However, I agree that the extractor might be secondary to a gas problem.  As I stated earlier I would double check the gas tube roll pin and make sure the gas tube is installed right-side up.  I'll think about it some more over lunch

Yeah, I see what you mean about the extractor. However, we just replaced the claw and the spring with brand new ones from Bushmaster. When the gun doesn't short stroke it ejects fine. I think that one shell was left in there because the bolt was cycling slowly and let go of the casing before it was lined up with the ejection port. It did lock back, but I think it had barely enough momentum to lock, and not nearly enough to kick out the shell.

Hopefully Tweak will be along soon and can help shed some light on this but in the meantime, can you guys pull the gas tube?  

If the gas key is tight and it doesn't appear to be the BCG then I'd start looking at the FSB and gas tube for the problem.  Maybe the gas tube has a kink in it, maybe the gas port in the barrel isn't in spec, maybe the hole in the FSB is clog up...I'd look for all those things and anything else that seems out of place.  

Yeah..  unfortunately I'm at work at the moment.  I'm pretty anxious to get a look at this and figure the problem out.  I feel like it's gotta be pretty close now.

No heavy buffer or buffer spring, they're stock as is the extractor.  The jam doesn't look like that, actually.  The spent casing will be inside the chamber partially- from 1/3 still in to 2/3 still in the chamber.  The next round will have it's point driven up underneath the spent casing and the bolt will be stopped behind the stuck live round.

It looks like the extractor is slipping off and the bolt is moving without the casing.  However, that seems suspicious because while testing with one round in the magazine we only once got a casing that wasn't ejected without the bolt locking back.  That one was extracted fully, which is not typical, but wasn't ejected.  It seems as long as the bolt moves all the way back, it extracts and ejects fine.

As my friend put it above, "When the gun doesn't short stroke it ejects fine. I think that one shell was left in there because the bolt was cycling slowly and let go of the casing before it was lined up with the ejection port. It did lock back, but I think it had barely enough momentum to lock, and not nearly enough to kick out the shell. "  Then again, maybe we have both an extraction and a short stroke problem compounding on one another.  But neither of us are experts.

Also, maybe it's just escaping me right now but I don't know  what HS stands for.

I've checked the gas key, it's solid.

Quoted: No heavy buffer or buffer spring, they're stock as is the extractor.  The jam doesn't look like that, actually.  The spent casing will be inside the chamber partially- from 1/3 still in to 2/3 still in the chamber.  The next round will have it's point driven up underneath the spent casing. Maybe it's just escaping me right now but I'm not sure what the HS is. I've checked the gas key, it's solid.

Damn, that just sounds like the typical extractor having a weak spring problem.

Short stroking, humm, I may have missed this, but have you used XM193 or like ammo that is a little hotter? What ammo are you using? Some of the Roadway on the Green British surplus ammo was under powered for their bullpup. Just a shot in the dark.

Quoted: This is why I still think there might be some sort of extraction issue: with the exception of one time when it locked back and the shell casing was floating inside, totally clear from both the bolt and chamber but had not been kicked out. That sounds like a classic weak extractor spring issue...the extractor can't hold onto the case long enough for the ejector to do it's job. However, I agree that the extractor might be secondary to a gas problem.  As I stated earlier I would double check the gas tube roll pin and make sure the gas tube is installed right-side up.  I'll think about it some more over lunch

If the gas tube is installed upside down the bolt would not move at all when fired.  Change your extractor, extractor spring and insert to correct one problem.  There have been some cases of the carrier key bolt breaking yet still be staked properly.  Get a gunsmith to check this.  Last and most importantly take it to a gunsmith familiar with AR 15s and let him open up the gas orifice.

37Victor - Here's a good thread where Tweak was addressing another short-stroke issue and I thought you might find it helpful: www.jobrelatedstuff.com/forums/topic.html?b=3&f=66&t=251525

I particularly like the idea of using a drill bit to ensure the FSB gas port and gas tube hole line up properly.  

I do not think the problems are with his bolt carrier group as he did but his bolt carrier group in another rifle and everything worked fine, even when held loose.

His problem is somewhere else on his AR.

Did you ever use a 22 cal conversion kit on your ar?

Quoted: Quoted: Last and most importantly take it to a gunsmith familiar with AR 15s and let him open up the gas orifice. it was hard for me not to use the Edit function on your post terrydavis. opening the gas port is ALWAYS the last thing to recommend in cases like this as it is the rarest cause of short strokes. once done it is not easily undone. as a rule 14.5" barrels overfunction so opening the gas port is strongly not recommended unless the gas port is proveably small to begin with.

I'm happy you didn't, since I am a professional gunsmith specializing in AR 15s.  I am a graduated of the Colorado School of Trades in Gunsmithing a Bushmaster/Blackwater and Colt certified Armorer and I have been doing this for the last eleven years.  I am sure I know what I am talking about even if you are not.  You will also note I said take it to a gunsmith familiar with the AR 15 system.

Quoted: I do not think the problems are with his bolt carrier group as he did but his bolt carrier group in another rifle and everything worked fine, even when held loose. His problem is somewhere else on his AR. Did you ever use a 22 cal conversion kit on your ar?

I agree but I would still advise 37Victor to replace the extractor spring with a Colt HD or a Wolff.  I would also follow Tweak's advice and install an H buffer.

IIRC his rifle would fail with nwmanitou's BCG installed when held loosely...no?

I would start at the FSB and work my way back in my hunt for a gas problem.

Well, on considering this last night I decided that the problem seems almost certain to be in the gas system, and that passes my ability to competently work on the gun.  So I contacted a well respected local AR armorer last night and dropped the poor little thing off with him this morning.

I would still like to get that Wolf heavy extractor spring, as I think it can't hurt and would likely give me a little more security, but I'll let the gunsmith check everything out and see what he comes back with.

I appreciate all of you guys' experience and advice.  I started off thinking this was some sort of weird failure to extract and never even realized I had a short stroke problem.  On my own I was headed in what would now seem to be totally the wrong direction.  Once this thing gets fixed I'll be sure to post here and tell you what he did to get her working.

Oh, just to reiterate for some of you guys who are curious now:  The ammo I typically shoot is Black Hills 68 grain heavy match.  I replaced the extractor and extractor spring with brand new ones from Bushmaster, no change.  I've swapped out the bolt/carrier group with a friend's AR with continued failures in my gun and continued good function in his.  The whole rifle is Bushmaster stock, with no work done on it except to add stuff onto the top rail.  Think that answers all of the recent questions!

ETA: Oh, and I've never used a .22 conversion kit on it.  What would that do to it, just out of curiosity?

With a 22 cal conversion, if you fire enough of the wax coatted lead longrifle loads you can plug up the gas system, either fully or part way.  

Wow, I never thought of that.  Good to know!

I've never done it, of course.

A 10 cent #60 O-ring installed around the outside of the extractor spring will add tension to the existing extractor spring.  This will tell you if the current spring is too weak, and/or allow the rifle to run long enough to allow the chamber to self-polish threw live fire.  If after 300 rounds when you pull the O ring (band aid) back out, the dropped/failure to fully extract and retain the case to the end of stroke problem comes back, then either the extractor spring is just too weak for the rifle or both the spring and the extractor needs to be replaced.


Right off the bat, the term Oil was used.  Unless you are using CLP (BreakfreeCLP) to clean and lube the rifle, then the current oil you are using may be the problem.  Lubes like Hoppes gun oil gum up way to fast when used in the rifle (gas gun) since they lack any cleaning properties (read continue to dissolve fouling as they are used as a Lube).  If you have not been using CLP as the lube for the rifle, then you need to flush the old oil (non CLP) out of the rifle, and lube the rifle correctly (read both clean, then lube the rifle with CLP). The reason that I state this, is when the bore of the barrel is cleaned, a copper solvent is required.  This is normal practice, but the copper solvent must be flush out of the bore/chamber or the solvent (like Hoppes bore solvent) will gum up if not flushed out of the system during cleaning.  

When cleaning the rifle, start off with the bore using the copper solvent, and then once you have finished the bore, step into cleaning the rest of the rifle with CLP.  This will allow you to not only clean the rest of the rifle, but also flush out any copper solvent that may be left in the chamber using CLP as the last step as well.

Note: In a few manuals you will see the term LSA used.  This Pre-CLP Dated lube was used to lube the rifles way back, but was replaced with CLP.  LSA is still available, but in regards to the AR system, CLP Is the specified Military lube/cleaner.

I use CLP for the AR.  I didn't know that about Hoppes, I use Hoppes on my revolver and .45/70.  Just seems to work better on them.