AR-15 rounds sticking in the chamber, please help.

[insidious_calm]

My brother bought me a Rock River arms CAR-UTE upper for my pre ban Colt. The upper sat unused in the packing for almost 2 years before I finally got around to putting it on along with a 4 position collapsable stock and new buffer. All parts were purchased new from RR. The problem appears to be rounds sticking in the chamber. Most of the rounds look like the case rims are damaged and on some the ejector has torn a piece completely out. Sometimes that happens and the old casing is still in the chamber when the bolt feeds a new round causing the new round to jam up on the old casing.

I have cleaned and re-cleaned the chamber. The rounds appear to hand cycle just fine. The upper only has about 100 rounds through it. Is this something that will "shoot itself out" over time? I'm a little nervous about the new rounds jamming up on the spent casing. Any help or advice is greatly appreciated. Thanks.

-IC


Edit- Forgot to add that I'm using new Winchester 55 grain fmj ammo.

 

[Hkmp5sd]

You need to check the headspace. Sounds like the chamber is too small. It will not fix itself and can damage the gun if you keep shooting it.

 

[4v50 Gary]

If rounds are sticking in the chamber, clean your extractor first. You may have to replace it or the spring or both.

 

[B27]

Is the upper marked .223 or 5.56mm?
If it is marked 5.56 I'd try running some milspec ammo through it before doing anything else.

 

[DMK]

The upper sat unused in the packing for almost 2 years before I finally got around to putting it on

I don't know if that barrel has a chrome plated chamber. If not, it could have developed some slight corrosion(rust) while sitting. If it's not chromed, you may want to polish the chamber.

I make it a habit to liberally oil and plastic wrap any parts that I store even if only for a short time. You can't always predict when a project will get shelved for much longer than predicted.

 

[Bartholomew Roberts]

Sounds like overpressure in the chamber to me... the extractor is getting a good bite on the brass since you mention it is ripping chunks out. The problem is the gas pulse is cycling the bolt backwards while there is still enough pressure in the chamber that the brass is adhered to the walls of the chamber.

That problem is very common when you fire 5.56mm ammo (Winchester Q3131A 55gr is one example) in a .223 sized-chamber. Because .223 has a different throat than 5.56mm, the pressures build up higher.

Try it with some Winchester Value Pack ammo or the 45gr varmint loads (you can also substitute American Eagle, or anything labeled .223 instead of 5.56mm). If you are still having trouble with those types of ammo, you either need to delay the gas pulse with a Fat Boy gas tube or heavier bolt carrier, or you can ream the chamber so that operating pressures aren't as high.

 

[Jim K]

All good ideas, but I think I will vote for polishing the chamber first, especially as the upper sat for 2 years and may have picked up some rust. The extractor and gas system are working OK, since the extractor is ripping chunks out of the rims. Polishing is simple; use a bit of 600 grit emery paper in a split dowel rod for about two seconds with an electric drill, then switch to 1000 grit for another two seconds.

If that doesn't work, and an ammo change doesn't work, you might also check the gas port size; an oversize port or one too close to the breech can cause those kinds of problems also.

Jim

 

[Bartholomew Roberts]

Check out the post by 4570Rick in this thread also:

http://www.thehighroad.org/showthread.php?s=&threadid=80843

 

[TonyRumore]

Polish the chamber

The correct fix is to polish the chamber. Whoever chambered the barrel, was lazy and did not clean up any tool chatter or scratches left by the reamer.

Tony Rumore
Tromix Corp
www.tromix.com

 

[insidious_calm]

Thanks for all the help....

I think I may have it fixed. I tried to polish the chamber as best I could for never having done it before. It seems to have worked. I put 120 rounds through it from the same case of winchester ammo and not one malfunction. I was shooting Winchester Q3131A though and I guess I don't understand exactly what the difference is between .223 and 5.56mm. Perhaps you could expand my knowledge of that? Thanks again. You all were very helpful.


IC

 

[Bartholomew Roberts]

Here is a good link on the 5.56mm vs. .223 chamber:

http://www.winchester.com/lawenforcement/news/newsview.aspx?storyid=11

 

[insidious_calm]

The barrel is not marked!

I had to go look after reading your link. The RR barrel is not marked. I looked under the handguards too. Their website states this particular upper is .223/5.56 NATO. Aside from inserting a 5.56 chamber ream(which I don't have) how can I tell what I have? Looks like I need to call them.


IC

 

[Bartholomew Roberts]

An easy way to tell is to fire some 5.56mm ammo (Wnchester Q3131A and Federal XM193 are two examples). If those rounds cycle OK, then it really doesn't matter what the chamber is, as long as function is good.

If those rounds don't cycle OK, show signs of blown primers, etc. then try the .223 loads (American Eagle, Winchester Value Pack, Wolf). If your gun cycles the .223 loads OK but not the 5.56mm, then it is likely a .223 chamber.