I recently built an upper with a Faxon 18" SOCOM profile barrel in 556 with a rifle length gas port. I used a standard non-adjustable gas block. The lower used a standard carbine buffer and spring. The rifle was way over gassed and I contacted Faxon and they told me that barrel had a .098 gas port. I increased buffer weight to 5.8oz until ejection was at 3 o'clock and function was perfect. The bolt was still getting excessively dirty so I purchased an adjustable gas block (Kaw Valley precision) from AIM surplus. I ran the upper on an old rifle lower I had just for comparison and it ran petty much the same.

Using a new gas tube for the install and going back to 3.1oz buffer I went to test the rifle with 4 different kinds of ammunition. Running the initial shot with closed port, each shot thereafter I opened the port a single turn of the adj screw until it was almost out of the block with no last round lock back nor feeding the next round.

Thinking the block was not aligned properly I disassembled it. Although not centered, the port was 100% inside the hole on the gas block (carbon circle around the port hole being at 6 o'clock in the circle). I inspected the block's hole as best I could for metal flashing debris etc, checked gas rod holes/pin alignment and orientation and reinstalled it with a drop of blue Loctite on the adjustment screw threads to keep a little more tension.

After repeating the same test process with the adj screw barely in the threads only the hot Fed M855 would cycle enough to hold the bolt on an empty mag and feed next round but not reliably. Ejection was perfect 3 O'clock. It went from over gassed to under gassed and the only things different are the new block and gas tube. I am out of ideas here.

What's next?

If you were extremely overgassed with a standard block and you’re now extremely undergassed with an adjustable block wide open, something has to be off with the new block or tube.

Any excessive gas leakage around the tube at the gas block?  Or around the block/barrel interface?

You’re either losing gas somewhere or your block is defective and isn’t actually fully opening.  Don’t really see how it could be anything else.

No excessive leakage on the tube nor the block. I emailed Kaw Valley the same info to see if they will send another block to try. I've seen mis-drilled gas tubes before but this one I inspected prior to buying to make sure it was good to go.

I don’t use adjustable gas blocks so what I am going to say may be totally out to lunch.  I have heard of some cheaper adjustable gas blocks having two set screws, the first one to lock the second one in place.  You remove the first, make adjustments to the second then lock it down with the first set screw.  I’m likely full of beans about this but you might check if your block uses two screws.  I’m sure that would be mentioned in the directions though.

No visual burrs can be seen. Sealing is good at all connection points of tube, block and barrel. The surfaces were pretty clean after 20+ rounds.  I used the loctite on the 2nd go around since the adj screw was pretty loose. I used just enough to seal the threads a bit and keep it in place.

Single screw design. The block didn't come with directions so I called Kaw Valley precision prior to the install.  They were more than happy to answer my questions. Thanks.

the gun was functioning perfectly so you changed the gas block because the bolt was getting too dirty?
it's a DI AR; the bolt will always get dirty

yes, excessively dirty. More so than all my others. I get your point though. Sometimes we should just leave things alone.

They actually told you that barrel had a .098 port?

I'd have sent it right back to them.  That is all kinds of wrong.

That's seems to being the ballpark for an 18"/rifle gas barrel ?

Seems like this must be something with the block.

I would try blowing through each block/tube assembly to see if the Kaw Valley is harder to get air through all the way open. If it is, then something inside the block is restricting the gas flow more than it should.

I was tired of messing around and I swapped the adjustable gas block with another standard low profile gas block from Luth AR. Went to the range with some M193 and my own mid level handloads and the rifle performed flawlessly.

no more gas system woes. $20 fix. Saved the AGB for another day when the can finally arrives. I may need it.