Hello all, I'm new to the site!  I've got a few questions that I was hoping that someone could help me with.  I recently finished building a 10.5" ar pistol in 556.  Today I took it to the range and had several FTEs.  The pistol is a PSA complete upper and lower.  The only changes that were made to the pistol was adding a Troy 11" alpha rail, removing the front sight post and added a low profile gas block, and I removed the A2 flash hider to install the KAK flash can.  A guy at the range said I needed to get a pistol length pigtail gas tube!  Will the pigtail fit under the Troy alpha rail?  Another guy said get a heavy buffer!  Then another said get the pigtail, adjustable low pro gas block, and the heavy buffer.  Not really sure what I need to do but would love some feedback because I want this problem solved.  I'm wanting to see if I should get all three items and if so will the pigtail fit inside the slim alpha rail.  Thanks ahead!

DO NOT get the pig tail gas tube.  Put three rounds in a magazine, describe what happens after each round shot, and after the last round shot, let us know if the bolt locks back...

 

Thanks for the reply!  I tried several things today.  The FTE didn't happen every time.  I put 20 rounds down the pipe using one pmag without any problems.  After the last round was shot the bolt did lock back.  The first mag was loaded with PMC brass.  The next pmag had five rounds of Tula.  The first to rounds ejected, then the third round that I fired didn't eject and the fourth round got hung up trying to cycle.  I tried using PMC ammo again and it started the FTE again.  Also tried using xm855 rounds and it had problems ejecting too.

Could be a variety of things.

Did it work before you  changed out the gas block?

Is your gas block properly aligned?  Usually that would mean not up against the shoulder of the barell.  

What buffer are you using now and with what ammo?

I'm using a regular PSA carbine buffer that came with the completed pistol lower.  I believe the low pro gas block is one correctly but I will be checking that again!  Why shouldn't I get the pigtail?

The pigtail is a gimmick.  You are probably a bit over gassed and may need to get a heavier buffer and/or upgrade your extractor spring...

 

I'm guessing yes. Or would have. There are a ton of the PSA 10.5" A2 sight base block uppers out there and this is first reported prob with one that I know of.

Gas block not aligned, not tight, or out of spec my guess.

OP, AFAIK all the PSA 10.5" barrels are carbine gas length, you can't use a pistol length gas tube on it!

- OS

I'm thinking of buying a h2 buffer and adjustable gas block.  Should I try this first?

I never ran the pistol before I changed the gas tube.  I didn't have the bcg so I couldn't.

If you're running a carbine buffer now, get a H3 so you'll have the ability to try all buffer weights from carbine through H3.  I wouldn't think you'd need an adjustable gb...

 

When I built my 10.5", I had issues with FTE and FTF and bolt not locking back. I took my upper apart and measured my barrel gas port. It was small so I opened it up a little bit and have not had an issue with Tula or any other ammo since. Changing buffers, gas blocks, extractors and all that will do nothing if ur not getting enough gas. Ur gas block may not be lined up perfectly either, since you have shot some rounds, when you remove your gas block you can tell where the gas is leaving a "ring" on the barrel. If that ring of gas is not lined up perfectly with the opening in your gas block, you should adjust it so that it is.

The gas block is typically spaced forward the thickness of the handguard retaining ring. Changing to a free float means the gas block isn't spaced back from the shoulder the thickness of the ring. Since we are talking in terms of mulitples of .010" having the gas block back too far will obscure the port.

Move it forward away from the shoulder the thickness of the guard ring and it places the port directly under the block opening. Ignoring it means chasing your tail making changes and spending money on things that still own't fix an elemental part relationship that was disturbed.

On barrels dimpled for clamp on gas blocks the better makers move it the required distance forward and there's no issue. It's almost always a converted barrel that this essential finesse point is missed.

They may be Legos, they aren't entirely that easy.

Try a # 60 o-ring around the extractor spring. I keep a bag of them in my bag when I hit the range, quick and easy fine tuning.

I run one in my 5.56 and 7.62 pistols, heck even slapped one into my brother's pistol too.

I just saw a video on YouTube of the o-ring install on the spring.  I was hoping you could tell me why this helps?

Added a PSA H2 buffer and the problem was resolved.  I've ran 200 rounds of tul ammo down the pipe and 150 rounds of 55 gr PMC ammo.  No issues whatsoever!  Happy with the finished product.  I'm going to start a new build in Jan and have a buddy who cerakotes so the build will take a little longer.  Will try to post some pics of the pistol if I can figure out how to add them.  Sorry I'm still new to this, but here is a parts list:

Upper:
PSA 10.5 CHF complete upper
Troy low pro gas block
11" Troy Alpha Rail
Inforce FDE wml
KAK flash can
Magpul FDE front and rear buis
BCM large latch charging handle
PSA NiB BCG

Lower:
PSA Complete pistol lower
Magpul FDE MOE pistol grip
FDE sig brace
Phase 5 multicam sig brace straps
Magpul BAD lever
Random multicam 2 point sling
PSA H2 buffer

Very similar to the setup I had for a while. Then I got tired of the Troy Alpha rail feeling like a cheese grater.