I just built an AR,  It's got a Doublstar lower, and everything fits together just nicely.  

I tried 4 different types of ammo in it and none of them would cycle the bolt completely.  50% of the time the spent shell would not eject, and the other 50% the spent shell would eject but the bolt did not come back far enough to strip a new round into the chamber.

I've got a 6 position collapsible stock with the buffer that came with the stock.  Am I correct in thinking that the buffer or buffer spring could be the problem here?  

What change would you recommend to make this thing run?

Thanks.

(Oh, and I had this username before Barack Obama bastardized it.  Please don't think it is any kind of endorsement of his ideas or presidency.)

Situation has been updated, but problems persist.  See new post below. (about 6 down)

When you pull the charger back, does it lock on the bolt face or on the bolt carrier group?  If bolt carrier group, your buffer spring is too long.

I had a buddy with this same problem on a new upper he bought. After looking things over and realigning his gas block, cleaning the shit out of it and countless hrs of frustration. he sent it back. Ended up being an out of spec carrier, thing would cycle fine by hand, but once you tried to throw rds, it would bind enough to raise hell. You happen to have another or a buddies carrier to try just to eliminate that possibility?

You've been around here since 08 and this was your 1st post? Damn man, I thought I had nothing say most of the time but you take the prize!!

I vote gas block:-/

I've been busy reading.  

Thanks for the feedback on the issue.

Sounds undergassed. Did you get an off-the shelf upper (and from what company), or put it together yourself? Standard front sight tower?

Yep, I had this issue when I used a two piece YHM gas block on my first build.  You can see how dirty the gas tube is if it is new it should not be that dirty.  What kind of gas block are you running?

It would make a perfect wall hanger........


Sorry, I have nothing of value to add. I hope you get it figured out.

I assembled the upper,  but not the bolt carrier group, that was an off the shelf buy.

The bolt catch does properly catch on the bolt face, not the carrier.

The gas block was a 4 rail block that was clamped, it was not leaking around the block.

BUT, I swapped out the gas block for a NM standard front sight.  problem persists.

I pulled the upper apart and there was some wear in the top channel of the upper where the charging handle rides. nothing major, but I then spotted that the charging handle was cracked at the front where the gas tube penetrates.  I replaced the handle with an unused one.

I'm thinking the bolt may not be catching enough gas.  How much lube can I put on the gas rings?  So i use a grease, or an oil?  

how do you feel about a CLP product in this location?

Break free CLP? It's good enough for some of our military.

What manufacture is the barrel? Are you sure the gas port is lined up with the gas block? Gas rings look ok? Is the gas tube fitting into the carrier key ok?

You can wet the entire bcg pretty good. Not dripping but Slip 2000 or CLP so its wet to the eye and touch. If you look in the M&C forum, there is some good info there.

I recently assembled a Dissipator with a cut down 20 barrel and an A2 stock and had pretty much the same problem.  At assembly I enlarged the gas port to .110.  Came home and finally enlarged the gas port to .120 and it ran fine on LC, Win, Guat, and Academy, ammo.  Using Wolf ammo sometimes the carrier needed the foward assist.  The only thing lubed was a slight oil from the new BCG.

Maybe your gas port needs to be slightly bigger.  Are you using a 16 in barrel with a carbine gas system?  If you have a good set of drill bits determine the size of your gas port and goggle port sizes.  That's what I did the information I found is what detemined the gas port size I used.  Hope that helps.

You don't say what ammo you are using ?......use good high pressure ammo like XM193 or M885.

Verify gas port - gas block alignment

Verify proper gas tube installation

What buffer are you using ?

I had the same problem and had to increase the gas hole one size larger but I should have tried a softer buffer spring first//// Before you do anything... Pull your charging handle back and look in the ejection door and make sure you bolt goes back about 1/4 inch from hitting the bolt lock and make sure you have nothing in the buffer tube that is stopping the buffer from going all the way back... I have seen on some guns the Twang buffer was stopping the buffer or spring from seating right.... like every 3rd or 4th shoot.....

I had a similar issue with a new build about 6 months ago using a DD barrel.  The gas port was way undersized.  I stuck a drill bit in there and turned it by hand to open it up (removed some of the parkerizing). No issues since.  Sorry, but I forget the diameter it should beat and maybe somebody with more knowledge could weigh in..  I want to say .0625" for the carbine length system.

I also had a buddy who was experiencing some issues with one of his new builds.  Found it was his accuwedge rubbing the bottom of the bolt carrier.  Not sure if you dropped one of those in there, but just throwing out a couple things to check.

Gas port sizes are:

11.5" barrel, .625: dia., 3.850" from muzzle;
Port sizes from .081" to .089"
11.5" barrel, .750" dia., 3.850" from muzzle
Port sizes from .086" to .094"

14" barrel, .625" dia., 8.375" from muzzle;
Port sizes from .063" to .078"
14" barrel, .750 dia., 8.375" from muzzle;
Port sizes from .070" to .086"

16" barrel, .625" dia., 8.375" from muzzle;
Port sizes from .063" to 078"
16" barrel, .750" dia., 8.375" from muzzle;
Port sizes from .070" to .086"

20" barrel, .625" dia., 8.375" from muzzle;
Port sizes from .086" to .093"
20" barrel, .750" dia., 6.875" from muzzle;
Port sizes from .093" to .096"

24" barrel, .825" dia.,
Port size .089"


That being said .... check your gas key and screws .... make sure the key is properly mated to the carrier and the screws are both tight.

As far as lube goes ... like CLICKBANG said Slip 2000 and CLP are both GTG.