I installed a new 18" AR barrel, 1:7 twist, chrome-lined. Headspace is perfect. Gas port was drilled at 90 degrees and to just a hair larger than spec. New build Torttort, Red Arms AK SA trigger.

Got out the other day for testing. Wolf steel 223 would not cycle great (~50% FTE), brass-cased AE 5.56 55gr cycled most of the time.
I know the Wolf is less powerful from use in a variety of other platforms.

Gas piston head had ample residue on it, meaning the gas is getting there- its either now enough gas OR the bolt carrier is not as smooth as it should be.
The residue did not appear to be making past the piston head much though- which would be consistent with not getting enough pressure to move it.
Many of the FTEs were just from the bolt carrier not moving at all.

I don't think the trigger group is the issue, functionally it's smooth. The bolt carrier does need to reset the hammer and maybe that's where the drag is coming from(?). Original parts kit hammer spring seems fairly light. Cases are NOT getting stuck in the chamber.

I'm left with the ideas of either weak gas OR something on the bolt carrier making too much drag.

Pondering getting a KNS adjustable piston, but for the inverse of what most people want to do (I want to increase gas pressure).

Any other ideas?

Have you tested the bolt carrier by itself for drag spots, or making sure there is no binding spots? I had a Hungarian AK BC/and bolt that would hang up on new build with a Childers receiver once, but when I swapped the BC with another Hungarian Carrier it worked fine. For some reason that carrier liked the twist itself ever so slightly on initial release that it was hanging up in the rails. I haven't taken the time to find out why as I just said screw it and swapped it and will figure it out when I use it for the next build! You can also polish the top of the hammer and the underside of the bolt carrier, I had to do that with an AK once.


ETA did you try it with any other ammo besides Wolf? You could try a weaker spring maybe? I've got one Galil that will not run on anything other than IMI or Federal brass 55 or 62gr ammo. It wont cycle the steel stuff worth a damn, but I don't shoot it enough to really care.

I just had it apart and yes- there is a healthy amount of drag on the bolt carrier from the hammer. The hammer contacts the underside of the rear of the bolt carrier as it moves back, hammer moves down (but its enough that I could see how the gas pressure might not overcome that every time), then as it continues back, the front edge of the bolt contacts the hammer and slides past, again needing to push the hammer down a little further than the disconnector is holding it.

This is Red Arms adjustable trigger, but I don't see a way to get the disconnector to hold down the hammer more.

And to clarify- yes, Wolf crap is less powerful and did not cycle ~50% of the time.
AE brass 5.56 M193 cycled much better- not perfect, but most of the time fine.

Bolt carrier is very polished as its FA surplus.
Hammer face is very polished.
Everything is square, no sharp hang-ups cycling by hand.

Just the pressure of the hammer pushing against the bolt carrier and then the bolt is what is holding it back from fully-cycling.

I do have another bolt carrier from a SAR, I can test it without swapping pistons to try it by hand for any difference.
I still think either gas more gas pressure in there OR getting that hammer down more is the way.

I would try the other BC first. That is an expensive trigger to be messing with.  Another thing I forgot to mention in the first post was I did have an AK back in the day that I actually had to shave the hammer down a bit to get it it to function because it was doing the same thing yours is. it worked fine after that though. Forgot about because I traded it off many moons ago, but that was with a cheap century trigger group. I'd try everything else before I did that to an RSA group.

Cool, thanks for the input- I may switch triggers here.
I can put in the original surplus trigger group just for comparison quick cycling it by hand to see if there's less resistance from the hammer, too.

Ok, just quickly swapped over to a surplus SAR bolt carrier with same bolt and the hammer drag is WAY worse.
Definitely focusing on the hammer now.

That would be a good test

is the bottom of your bolt binding on the bullet guide?  Particularly as the bolt rotates into lockup?  If it is you usually can see rub marks on the bullet guide.

Nope, bullet guide all good.

I compared the FA surplus hammer to the Red Arms trigger and the later is overall thicker to the hammer face, also has two distinct angled humps that I can feel while cycling.
The FA OE hammer is a smooth contour all the way across the hammer face and is lower-profile.

This is definitely all about the hammer making resistance against the bolt carrier and preventing full cycle. Symptoms are FTE without a round sticking in the chamber.

Out of time to fiddle with this for now, but will definitely be trying the OE hammer to see if I can get a smoother cycling by-hand, then do range test.
If the OE FA hammer works, I'll probably just trim on of the tabs off like SA hammer so there's no confusing intent.

Thank you all for the input.

Here's a comparison of the Red Arms hammer, an AR surplus hammer, and a SAR surplus hammer (which has a nice groove running down its length from wear).
Note the contour differences.


https://i.imgur.com/GIdXxXL.png
https://i.imgur.com/V5bikEc.png
https://i.imgur.com/NJUI13q.png