I have a funny situation.

I have a Bushmaster AR-15 Post Ban 20" HBAR. It runs without any problems with UMC, Sellier and Bellot, and Wolf. However, whenever I put South African M193 surplus or Winchester white box in it, it short strokes or fails to extract (resulting in a fired shell and live shell trying to enter the chamber simultaneously) almost every time. After my rifle jams with these brands of ammo, I take out the magazine and put it in my friend's or uncle's rifles, and it runs through without a hitch. As soon as I swich brands back to Wolf, S&B or UMC, it runs like a champ again.

This is the only thing that upsets me with this weapon. Especially since I bought a 2,700 round case of the South African stuff a few years ago.

Is it just as simple as saying that my gun does not like this ammo, or could there be some sort of abnormality in the condition of my rifle?

Any help is appreciated.

What magazines are you using? Try again with 20/30 round US GI mags.

(edited to add-)

Also check to see if your model DCM competition model with SAMMI chamber?

I fixed the same type of problem by drilling the gas port on the barrel. I went up 1 number drill size at a time....very little material being removed. This gives it a little more gas pressure with what may be under powered rounds...for your gun. (tighter chamber, heavier recoil spring, more blow-bye in gasblock/barrel area, etc...)

MY $0.02

It never fails. Everytime someone posts a problem with short stroking caused by the gas system someone will claim it is a mag problem.

Just what does the mag have to do with extraction and ejection?

Is the ammo PMP? I have the same problem with PMP in my Colt M4.

The PMP is a little underpowered.  My friend had the same problems with his 20" Bushmaster.  It ran fine on the Israeli made Winchester Q3131A.  

Detlef, after 1,000-2,000 rds through it, it should work on any ammo.  Also try leaving it on the bolt open position overnight before going to the range.  This will help break in the buffer spring faster in which the stiffness of a new spring may contribute to this problem with underpowered ammo.

Is it a brand new rifle? When I first got my Bushmaster I had a lot of problems with certain ammo. I would guess that parts just have to wear in.

I have a similar problem with my new DMPS CAR HBAR.  I bought the Winchester white box stuff and one or two failed to eject on almost every mag.  It was abit disappointing. Switched to UMC and S&B and they shot without a hitch.
My rifle has .223/5.56 stamped on it.  I called Dave at DPMS and he said that the white box Winchester has higher pressures which expands the casing causing it to wedge in the chamber which causes the ejection problems. So, I just stick to what works and maybe after a few thousand rounds or so, Ill try some other stuff to see if a little break-in period will help.
DPMS has a policy ,though, that states, You must use American made commercial ammo or it voids their warranty. (No Russian, South African etc.)

PS. I know S&B is not American made but it works. Just wanted to state that before I get roasted. I shoot UMC all the time. Had  only 100 rnds. of S&B.

     [heavy]

My friend had the same problem with his Carbon 15,the ammo just doesnt have enough power to cycle the bolt,I used the same ammo in my bushy without a problem.

There are a few things you can do in the meantime: get some of the long 'pipe cleaners' made for cleaning your gas tube and port. Shoot some 'Gunscrubber' or auto brake cleaner down the tube, then work it with the pipe cleaner. Check to see if the end of the tube is bent or obstructed. Make sure the gas path is open through the base to the bore. Take the bolt out of the carrier and thorughly clean and oil both assemblies. Make sure the three gas rings on the bolt are correctly oriented. Use a bore cleaner on a chamber brush and clean and lightly oil (then wipe oil out) the chamber. Take recoil spring out of buffer tube and swab out buffer tube with light oil. Clean and lube the upper. If it doesn't cycle after that, there probably is a mechanical problem as outlined by the others. The recoil spring may have to be tweaked a little. It is entirely possible that as you shoot and clean/oil over and over the problem will just go away as parts wear in and the spring settles down some. Still, the rifle should have been set up better than that. I built my own on a Bushy lower, never having touched an AR before, and it works great. I haven't found any ammo it doesn't shoot fine, including the 1980s Korean, various handloads, Nosler Ballistic Tip, M193 and M855, SS109, and others that I can't think of right now.
[img]http://img.villagephotos.com/p/2003-6/16185/CAR15a.jpg[/img]
   

Thanks for the replies, everyone.

My rifle has well over 1,000 rounds through it. The chamber is definitely mil-spec, but I agree, it may be a little tight. It seems that if this is my problem, chamber erosion from firing will naturally correct the problem over time. I will give the pipe cleaner chore a try.

Also take note that I baby this rifle. It gets every part cleaned and lubed routinely. I even clean the damn thing every once and a while just for the hell of it.

It is not double feeding or anything, so it is not a mag problem. I use only USGI mags. I have over sixty of them for one rifle, so I am a mag whore. Now I just need some more rifles.

If it is prematurely letting go of the empty casing, I would suggest an M-4 extractor spring and insert and possibly a new extractor before trying anything else.

Troy is right, forget the pipe cleaner.

Are you using a chamber brush?

[img]http://www.fulton-armory.com/ChamberBrush.jpg[/img]

Take a few pieces of cleaning rod and a chamber brush, stick in a varible speed drill, get some really good solvent and scrub the hell out of the chamber. run the drill at low speed and pull it back and forth in and out of the chamber, take an old chamber brush and wrap a cleaning patch around it, soaked in solvent, and scrub it again.

Replace the extractor and get a wolf heavy duty extractor spring.

If after that, it still doesn't run, replace the gas tube.

If it still gives you trouble after all that, send it back to Bushmaster.

If my Bushmasters eat Olympic then they it will eat
anything. But I do have a FTE every now and then. Sometimes because there's not enough pressure to extract, or at othertimes I think due to the chamber or shell casing heating up and expanding ever so slightly. I will usually have to take a cleaning rod and forceably pop one out if it won't fall out on its own.

Like Troy said, this is not a gas or short recoil problem since the rifle works fine with lower pressure stuff.  Could be chamber issue, but I would be surprise to find that to be the case if you are using a chamber brush to clean.

Generally, if the spent casing is left in the chamber and a new round is being chamber behind it, it is a extractor issue.  Either get a stronger spring, such as what Wolff sells or one of those d-ring things, or replace the extractor.  

If the spent casing is being extracted but being left in the receiver, then it is a ejector issue.  Either lube the ejector as spec'd in the military user manual or replace the ejector detent or spring.

Mags can effect functioning, but generally bad mags never lead to spent cases being left in the chamber or reciever.

I would suggest you check out the trouble shooting forum, you will generally get much better advice there.

This can still be a weak extractor spring and proabally is.  It is prematurely releasing the casing before the ejector can frimly push against the base and pivot it out.  It can be the ejector srping but, IMO is most proabally the extractor spring.  If it ain't ripping thru the rims, you cant rule out the extractor spring and it is your easiest fix.

An M-4 extractor spring is your cheapest fix to try as well and will hurt nothing to have in any event.

I agree. If you don't want to go that far, make sure you are using fresh ammo. Any that has been stored for ?? years may lose a lot of zip, depending on storage conditions. Definetly a gas pressure problem.

I had the same problem with a batch of South African I bought online... which Winchester "white box" are you using? The USA223 stuff or Q3131A? Mine eats Q3131A all day, it's Isreali made M193... the USA223 stuff sucks.

Correct. Bushmaster will tell you not to clean the gas tube themselves.