I spent an hour trying to get my new build to run.  Followed the instructions but it is not 100 percent clear to me.  I think the instructions all refer to the little screw and not the big one that keeps the gas piston in.

I understand turning the little screw 4.5 turns out is full open per instructions.  what if I turn it out more? Also what does the top large screw do when you turn it?  

I had the little screw at 4.5 turns when I quit after trying the top big screw in all positions. I tried many combinations but no luck.

I couldn't get it to lock back on empty mag or chamber another round but would eject most times.  

Help appreciated.  Running this on a 10.5 inch sbr with carbine gas system.  Was really wanting to shoot it today after waiting so long on atf to approve

I didn't want to take it apart to study it since its installed now

If i am understanding your questions correctly, the top "big screw" is designed only to retain the piston. Screw it all the way in, then back it off until the ball detent rests into the locking grove. The line cut into the hex socket should be nearly vertical.


Concerning the little screw, if you screw it all the way in clockwise, this is fully closed, no gas allowed into the gas tube, single fire only. if you then back it out 4.5 turns, the gas block is fully open. This is just like 90% of the standard gas blocks out there at this point. If oyu have set the detent at 4.5 out, your rifle should function at this point.

if you then continue to back the set screw out more, the block will start bleeding gas out the front of the block, instead of simply restricting or halting it in the barrel (often gas is pushed back into the receiver via the barrel as it has no place else to go). This is very helpfully for suppressed guns, lefties, and reducing gas to the face. But the gas allowed through the valve effects the rifle about the same either way.

I am not sure of your skill set, and please do not take any offense, as non is intended. I do strongly recommend you double check your block to make sure is it centered and seated properly. block alignment is critical to correct gas flow. Also, make sure you have a standard buffer spring and H1 buffer. The point behind heavy buffers is to reduce kick back because most rifle, including carbines, are over gassed. A heavy buffer slows things down a bit, But a piston gun, with an adjustable block, will not need a heavy buffer or spring.

Also, sometimes both the set screw model and clamp on model can shift during install. If the gas block covers the gas port on the barrel at all, you will have problems from the start.

Normally I would recommend a clamp on model gas block. But this is a piston gun. The set screw model has a slot cut to pin the block. Once you have you rifle dialed in, shoot it, and decide the piston system is the way to go for you, find a good gunsmith and pay them to pin the block. If you do not pin your gas block on a piston rifle, it WILL eventually come loose. Not the end of the world for a fun gun, but a big deal if your life depends on it. If you would prefer to pin it yourself, Brownells sells pins, jobber dril bits, and taper bits, its about a $30-35 dollar project fro the DIY'er.

BUT, take your time, go slow, and make sure you have a good vise on a drill press or a drill chuck on a mill. And some cutting oil. The gas block is hardened stainless, it take a slow cut to work through the metal.

I use the SA pistons on all of my SBR rifles, 10.5" 5.56, and 8-8.5" 300BLK. If you run subs on the 300BLK, you may need to open the gas ports up a bit and then dial them back down with the detent on the gas block.


If you check everything, all aligned right, standard spring an buffer, and you still have issues, you can always open the gas port on the barrel a bit. But honestly, you really should not need to do that on a 10.5" carbine barrel.

Let us know how things turn out.

Thanks I've installed many gas blocks before without issue, now that you confirmed my thoughts on the system and how it works I will check alignment again.  I always check alignment with 20 psi air hose or a short brass pin that drops out into the barrel

I did start messing with the big upper "screw" at the end, now I know that doesn't do anything but keep the piston in.  Maybe it reduced the efficiency by having it rotated out 1-3 turns.  It did work better before I messed with it the last 15 mins.  I will be using it with a supressor which is why I wanted to use the piston system with bleed off.  I could tell there was a change in muzzle blast depending on turning the little screw in and out so maybe I'm just slightly out of alignment?

Thanks

You don't mess with with the large screw.  Tighten it then back it off 180 degrees.

You should have an instruction sheet that looks like this:
https://suparms.com/pages/installation-instructions

As for the small screw it ships fully closed, back it off 4.5 turns to open it up, note that it is not fully open, this setting is called max pressure and it retains most of the gas to act on the piston the more you open that screw past 4.5 turns the more gas you bleed out through the block.  If you are not getting reliable action with it open to 4.5 turns then something is wrong.  Either the block isn't sitting over the gas port, the piston is binding/rubbing, gas port is undersized, the ammo is under powered, or any number of things that prevent the rifle from cycling fully.

Update, found a 5mm long burr on the edge of the vent hole on the side and it was causing binding part of the time when the piston went past the hole, now it's much much smoother.  Will test fire again this weekend.

Here is a video review/evaluation I put together is you want to check it out. https://youtu.be/HeKg0y628Bs

I took back out to range and now it works pretty good.  I'll have to lighten my buffer to get it to lock back on empty mag since I have added a law tactical folding stock that has the weight/spacer on the end of bolt carrier.  It works good just not locking on empty mags currently on full open

Did you get it running?  I'm having a similar issue.

You need more gas if it's not locking back!