I have a Bushmaster upper that exhibits failure to feed problems and would like your help to diagnose the problem.

The symptom is that I get failure to feed after around 100-150 rounds of use. The bolt would move the next round about .5 inch forward and it gets stuck. Pulling the charging handle and letting it go would always allow to round to properly feed. Fire the round and the next round would exhibit the same behavior. If I let the rifle "rest" for awhile, then it would function fine for awhile then back to the ftf problem. This has been a problem since I bought the upper brand new from Bushmaster.

Today, I narrowed the problem down to the bolt and/or carrier assembly. I swapped it out and used a different one (also from Bushmaster), and the "other" bolt and carrier assembly functioned perfectly...even after rapid firing three 30rd mags. My guess is it has to be something with the bolt and/or carrier assembly.

Do any of you have any thoughts on what could be the problem? It's as if heat has something to do with it. Thanks in advance for any help!

Some help for us is needed here. New or old? Has it behaved correctly? How many rounds since new? How many since you disasembled the bolt and carrier? Go to the top of this forum and print the checklist for function, then do the things on the list that can be done without ammo. Report back on any failure to behave.

Now on to likely causes...

Check (without ammo) that the trigger and disconnector are working properly: Clear Rifle of ammo and magazines; Open and close the bolt; Squeeze the trigger until the hammer falls and hold the trigger; Cycle the bolt manually while holding the trigger-the carrier should go home; Release the trigger - the hammer should reset with a distinct click; Squeezing the trigger again should start the process again.

If the bolt and carrier stops open with the bolt only part way forward, the hammer MAY have tried to follow the bolt down. The hammer has a notch that grabs the carrier when this happens, which is designed to prevent the gun from going full auto in your hands. If so, either the disconnector or the hammer or the trigger or all three or their springs have problems.

Get back to us with the results and we will go from there...

Hi Billski,

Thanks for your response. The checklist is currently out of order.

The upper was brand new from Bushmaster. The lower (actually, complete rifle) was new from a dealer. It has happened before, but I just brushed it off as a new rifle that needed "broken in". My test (by switching out bolt and carrier) confirmed that it's the bolt and/or carrier that's causing the problem. I don't remember how many rounds have been through the rifle. It doesn't have any problems when competing in CQB or slow target practice. It only has problems when just sending a lot of rounds downrange.

I tried your test suggestion and it behaves correctly. Should I be testing this with a "cold" rifle or when it starts acting up? Any other suggestions?

Is the next round stubbing on the barrel extension? If yes, you either have a mag problem or perhaps the rifle is short stroking a bit, and the ammo is not lifted all of the way to the feed lips before the bolt gets there. Why this would happen hot is beyond me...

Does the rifle always lock open when fired from an empty mag? If yes, look at your mags, if no, you are short on stroke sometimes.

On shorties, lots of folks have taken to polishing the feed ramps or even opening them up to facilitate feeding ammo from the mag to the chamber.

I just put a lengthy list of things to check on another note. Look it over and see if anything sounds familiar. Get back to us and we will get you running.

I don't know what "stubbing on the barrel extension" means. I definitely know it's not a mag problem since I tried 5 different USGI an Thermold mags. The rifle always locks open after the last round.

I'll check your other post.

I took my rifle down yesterday and realized that I remembered somethign completely wrong - if the hammer follows down, the bolt will NOT be caught where your rifle is stopping, it will be much closer to being closed.

The fact that the rifle always locks open is a good sign, it is cycling the carrier fully.

When I say stubbing, I mean that the bullet contacts the barrel extension (the part that the bolt enters and locks to) or reciever somewhere other than on the feed ramps.

Are the mags clean? If they are gritty, they could be wedging a bit and that could bind a round so that it is harder to get moving. GI and Thermolds can be disassembled and throughly cleaned, so that might be inorder. Some folks even put them through the dishwasher...

I am about out of ideas. Anybody else able to help out here?

Quoted: I am about out of ideas. Anybody else able to help out here?

Without seeing it, I can only offer some things to look at after reading the thread.

It still sounds like it's short stroking when hot.
I'd take a close look at the carrier key, see if it's tight, has the proper screws and the stakes are done properly. It's possible that the stakes are raised too high or put in the wrong place making the key "fat".

Mine was "short stroking" like that, it would jam the rounds into the feed ramp and sometimes would not lock open after the last round was fired. The fix? I replaced the gas rings.

The problem seems to have disappeared after following suggestions from Bushmaster's tech support. I have included the e-mail thread below your fyi. I don't know if the problem is really fixed or not since I didn't have the problem during the last range session. I'll try to post a followup message after my next range session...don't know when though.

>From: [email protected] >Subject: RE: Bolt and carrier assembly causing failure to feed >Date: Fri, 25 Oct 2002 10:34:29 -0400 > > > Should you experience any problem do not hesitate to call our >Customer Service people at 1-800-883-6229 to get shipping information and an >RMA number to send us the barreled upper receiver with the bolt carrier >assembly for correction under warranty. It would not cost you anything other >than shipping it to us as we would not charge for gunsmithing or parts >required to correct it and we would pay shipping costs back to you. > Thank you for your concern and support of our Company, Matt > >-----Original Message----- >Sent: Friday, October 25, 2002 1:46 AM >To: Matt Hasty >Subject: RE: Bolt and carrier assembly causing failure to feed > > >I followed the steps you have outlined and did not notice any problems. Last > >weekend I shot about 300+ rounds through it without a hiccup. I'm not sure >if tightening the screws had anything to do with it. It didn't seem loose >and I'm not really sure that it moved when tightened. If this problem >re-appears the next few times then I'll send the upper back for a >maintenance check. Does it cost me anything except shipping charges to you? > >Thanks for all your suggestions. Hope the killings doesn't affect your >business negatively. > > > >From: [email protected] > >Subject: RE: Bolt and carrier assembly causing failure to feed > >Date: Thu, 17 Oct 2002 14:04:31 -0400 > > > > > > The other things to check would be the feed ramps where the steel > >barrel extension meets the aluminum upper receiver. If there is a small > >step > >even .010" to .020" at the bottom of the feed ramps then blend it into the > >feed ramps at the same angle using a round stone or a needle file. > > The bolt carrier key should be checked for a gas leak as follows; > > First check to see if the bolt carrier key screws are loose by > >trying to tighten them with a 9/64 allen wrench. If the key screws were > >loose they need to be removed so the key can be properly reinstalled. > > To check to see if you have a leak at the bolt carrier key causing > >short stroking pull the bolt carrier assembly from the upper receiver. Push > >the bolt into the carrier and hold it there while performing this test. > >Spray a light oil into the key. Blow a couple of pounds of compressed air > >into the key. If you do not have compressed air place a rubber tube onto > >the > >key and blow into it. If there is bubbling between the key and the carrier > >it has a gas leak. > > To correct the gas leak remove one of the screws and put it back in. > >Remove the second screw then go back and remove the first screw. This gets > >the screws past the staking so that they will not be stuck in the key. It > >is > >best to lightly stone off the top of the carrier and the bottom of the key > >with a fine Arkansas stone that is flat and square to remove any possible > >high spots. Clean the key and the carrier with brake cleaner to remove any > >carbon build up. Put a drop of oil on the bottom of the key and wipe it off > >so that there is just a thin film left on it. Install the key by torquing > >the screws at 45 INCH pounds. The key can be restaked with a dull prick > >punch so that some of the metal of the key is pushed against the screw > >heads > >to keep them from getting loose. > > You can always send the barreled upper receiver to us for evaluation > >and correction. > > > >-----Original Message----- > >Sent: Thursday, October 17, 2002 1:33 AM > >To: Matt Hasty > >Subject: RE: Bolt and carrier assembly causing failure to feed > > > > > >Thank you for your suggestion. I checked both ends of the ejector pin and > >they are below the bolt face. I don't see anything visibly different when > >comparing two bolts side by side. Anything else I should try? > > > > > > > > >From: [email protected] > > >Subject: RE: Bolt and carrier assembly causing failure to feed > > >Date: Wed, 16 Oct 2002 14:57:55 -0400 > > > > > >         The thing to check would be to see if the pin ejector is sitting > > >above flush with the bolt face. The pin ejector should sit just below > >flush > > >in the bolt face. If the pin ejector is sitting high when the bolt feed > > >lugs > > >pick up the cartridge to be fed the head snags on the pin ejector as it > > >slides up and will not enter the pocket in the bolt face. Recharging the > > >bolt carrier allows the pin ejector to compress as the cartridge is at a > > >different angle to enter the pocket. Replacing the 1/16" retaining roll > >pin > > >will usually correct this problem. > > > > > >-----Original Message----- > > >From: Administrator > > >Sent: Wednesday, October 16, 2002 11:57 AM > > >To: Matt Hasty > > >Subject: Bolt and carrier assembly causing failure to feed > > >* RMA: > > > > > >* Product: Bolt and carrier assembly causing failure to feed > > > > > >* Remote Name: 131.107.3.78 > > > > > >* Remote User: > > > > > > > > >Question > > > > > > > > >I have a Bushmaster upper that exhibits failure to feed problems and > >would > > >like your help to diagnose the problem. The upper was brand new from > > >Bushmaster. The lower (actually, complete rifle) was new from a dealer. > >The > > >symptom is that I get failure to feed after around 100-150 rounds of use. > > >The bolt would move the next round about .5 inch forward and it gets > >stuck. > > >Pulling the charging handle and letting it go would always allow to round > > >to > > >properly feed. Fire the round and the next round would exhibit the same > > >behavior. If I let the rifle "rest" for awhile, then it would function > >fine > > >for awhile then back to the ftf problem. This has been a problem since I > > >bought the upper brand new from Bushmaster last year. Today, I narrowed > >the > > >problem down to the bolt and/or carrier assembly. I swapped it out and > >used > > >a different one (also from Bushmaster), and the "other" bolt and carrier > > >assembly functioned perfectly...even after rapid firing three 30rd mags. > >My > > >guess is it has to be something with the bolt and/or carrier assembly. I > > >tried different USGI and Thermold mags and each behave the same way when > >it > > >starts to ftf. Do you have any thoughts on what could be the problem? > >It's > > >as if heat has something to do with the bolt and/or carrier. I have also > > >seeked help from AR15.com members: > > >http://www.ar15.com/forums/topic.html?b=3 > > ><http://www.ar15.com/forums/topic.html?b=3>  &f=66&t=141230 Thanks in > > >advance for any help!