Got a odd problem, maybe one of you gentlmen can point me in the right
direction?

DPMS AR15 w/ bull barrel.  No mods, well maintained, clean, less than 1000
rounds.  With no ammo, weapon performs function check flawlessly. All
components apear to be within spec, no excessive wear or obvious problem.
Weapon shoots fine.  No function problems at all with a variety of ammo.
No problems shooting rapid fire.

However.  If I pull back the charging handle and load a live round, once I
release the charging handle, I cannot clear the weapon.  The bolt is locked
forward and will not unlock unless I either fire it, in which case it will
cycle fine and load the next round in the mag, or I shotgun it and use a
tool to leverage the bolt back.

I have removed the upper in order to clearly see the action while loading.
Placing a dummy round into the chamber and riding the bolt forward, it
appears that the bolt stops before fully locking. If I press down on the
bolt with substantial pressure, it will lock.  It will then stick and I am
unable to unlock it by simply pulling back on the bolt.

Any ideas?

Eric B.

You have very tight minimal headspace. Tweak is correct.

It happens with all ammo I've put through it.  I don't shoot any ammo with steel cases, and mostly what I shoot is .223.

When actually shooting, it functions fine, no problems cycling and the gun does not jam.  The problem only occurs when I need to clear a round in the chamber, that is when the bolt remains locked forward.

I'm not quite sure how to adjust the head space?  If it is a head space problem, it is just barely out of spec.  

This is the first AR I've owned, discount the fact I carried an M16 for 15 years in the Army, I've never seen this problem occur.

Also, on DPMS's website, they make a point in stating that all their standard barrels are chambered for 5.56 Nato, but their bull barrels are chambered for .223.  I do not understand why they make this distinction?

Eric

.223 and 5.56 chambers are different.

You can shoot 223 in a 5,56 but there may be a problem using 5.56 in a 223 chamber.

I had a 16" DPMS barel that would not headspace even after trying many bolts. Sometimes you can try different bolts and find one that will work. If not DPMS took mine back and corrected it for me. Spaced fine after getting it back.
Also got a Model1 7.62x39 barrel that is tight. Got some surplus last month and the bolt will not lock closed on some rounds and jams it up.

Quoted: I had a 16" DPMS barel that would not headspace even after trying many bolts. Sometimes you can try different bolts and find one that will work. If not DPMS took mine back and corrected it for me. Spaced fine after getting it back. Also got a Model1 7.62x39 barrel that is tight. Got some surplus last month and the bolt will not lock closed on some rounds and jams it up.

That's the same barrel I have, the 16" bull.  I just talked to a DPMS tech.  He said to use a power drill with a rod and borebrush on it and work the chamber with it for about 2-3 minutes.  If it didn't space correctly after that, he said he'd RMA it and have it fixed.  He said they run their tolerances tight and sometimes they get one just a little tight, 99% of the time the bore brush trick corrects the problem.

Eric

He said to use a power drill with a rod and borebrush on it and work the chamber with it for about 2-3 minutes. If it didn't space correctly after that, he said he'd RMA it and have it fixed

If your chamber is clean then this is a big waste of time.

What a bunch of crap. Feel free to ruin your chamber.

+1

I very strongly WOULD NOT advise that you do what the clown from DPMS said to do. You will ruin the chamber very quickly. Find someone with a chamber reamer of proper dimensions to clean it up properly for you. Semper Fi. Charles. A gunsmith.

Quoted: He said to use a power drill with a rod and borebrush on it and work the chamber with it for about 2-3 minutes. If it didn't space correctly after that, he said he'd RMA it and have it fixed If your chamber is clean then this is a big waste of time. What a bunch of crap. Feel free to ruin your chamber. +1

Actually if yu have a carbon buildup in the case neck and shoulder area of the chamber this works quite well as long as yu use a brass brush , good solvent and keep the rpms down. I've done this for years and have never had a problem with chamber damage of any sort.

If your chamber is clean then this is a big waste of time.