Just put together a DPMS 20" kit, and having some problems.  

When I was putting together the bolt/carrier, the bolt was quite hard to get into the carrier, and I was thinking it was just that the gas rings had never been installed and just need to be worked.  It would rotate freely without the firing pin, but was hard to move back and forth.  When the firing pin and the bolt pin was installed, it was still hard to move.

The kit I got had the gas block that tightens down with the two allen head screws instead of the regular front sight.

When I took it out to shoot it for the first time, I fired about 20 shots, and could not get to function correctly.  On a few shots the bolt would cycle about halfway and stop, and on all the rest it would not even move.  I took the gas block off to check the barrel's gas port alignment with the gas block's hole, and it was VERY close to right.  Just a tiny "half moon" of carbon off to one side.  I adjusted it, and the problem still remained.

When cycling the bolt with no shells it seems to function okay without excessive binding or scraping or anything.  It will slam home every time.  I haven't staked the gas key on yet but it seems to stay put so far.

On these new builds, do the gas rings have to wear in or should they work right away?  

I never had to deal with any of this with my other rifle since it was an early Colt that had already been used, so would appreciate some help.  

Son of Liberty,

A new bolt carrier build will be a little stiff but should wear in quick. Disregard the gas ring gap myth, that's left over knowledge from internal combustion engines. Once something gets written in a manual it's impossible to stop. The rings rotate as the bolt cycles and change their orientation and relatioship while doing so.

Does it pass the 30 degree drop check outlined in the 23&P?

Does the bolt carrier slide smoothly without the bolt? Does it slide smoothly with the bolt [b]by hand[/b]?

We've got a similar thread going in Troubleshooting right now. Dano has posted a pretty comprehensive list of checks [url=http://ar15.com/forums/topic.html?b=3&f=66&t=173550]here[/url].

I'd add;

Check the inside of your gas block. Make sure that the hole there lines up with the hole in the gas tube and there is no obstruction. I use a twist drill of the correct diameter to check both.

Check the ID of the gas tube.

Check the OD of the gas tube end that goes into the carrier. Compare that to the ID of the bolt carrier key.

Make sure your gas rings didn't get bent during install or firing.

Make sure that the ends of your gas rings are tangled or bent out of the groove they ride in.

There's more checks on the Troubleshooting checklist found under Rule II [url=http://ar15.com/forums/announcement.html?b=3&f=66&id=184]here[/url].

Thanks for the suggestions so far.  I'll probably get out to shoot the rifle again in the next couple of days and see what happens then post back here.

Thanks
SoL

If you were running the rifle with the proper amount of lube before, more shooting isn't going to change anything for the better. Your decision, of course, but I would personally do the checks above before shooting it again. No way to tell what's wrong with just the brief details you gave, but more shooting without diagnosing and fixing the problem could cause damage.

Just took the rifle out and shot it again today.  It seems the bolt and carrier is loosening up as the bolt will now move more freely, but the gas problem is still there.  The bolt and carrier will now eject almost all the cases, but won't travel far enough back to pick up the next round.  

I put some Lok Tite on the carrier key screws earlier today, so the key is nice and tight now.  

Going to take the gas block and tube back off and see if there is anything else I missed there.  It seems like the gas tube was flowing OK, but going to check again anyway.

[pissed]  Kick-@$$ looking single shot!

SoL

you're going to want to stake the carrier key screws, locktite won't do.

A quick question...

I took the gas block off to make sure there is free flow through the tube and gas block, and noticed that the gas port in the barrel is quite a bit smaller than the hole in the gas block.  

Can anyone tell me what size the barrel's hole should be?  

Edited to add:
Quoted from the troubleshooting page - "With the upper at a 40 degree angle to the ground release the bolt carrier and check that it locks fully into the barrel extension under its own weight."

I tried this, and the bolt would ALMOST go into battery, but not quite.  It lacked about 1/8 inch or so.  There is no obvious reason I can see why it won't.  Since I lubed it up good, it goes alot further than it used to.