Hello all,

I have a 7.5 in SBR that is using an adams arms pistol length system.  It is having an issue with short stroking.  The used casing is ejected correctly and with proper power and the trigger is reset, but the subsequent round is not picked up and loaded.  My trouble shooting began by removing the gas block and rechecking the gas alignment.  I used a bent paperclip to ensure that the gas port was linger up correctly.  Next i checked the movement of the piston to ensure it moves freely.  It passed my admittedly unscientific test.  I am using the lwrc stock that is shown here:

https://www.lwrci.com/p-361-uciw-ultra-compact-stock.aspx

This uses a proprietary tube, spring and buffer.  I have used this system before on a 16 inch rifle with an adams arms piston and it was fine.  BUT, it seems to me that the next most likely culprit in my situation is the buffer/spring combination.  The buffer itself is already pretty light, so i think my move is to trim the spring down and see if cycles correctly....does this sound right to the rest of the crowd?

Thanks in advance for the assistance :-)

Still wondering if it's getting enough gas, is the port the right size?  I don't know what it's supposed to be, just thinking out loud.

What's the buffer weight?

you are bringing up a good point.  I wonder what is the standard accepted gas port size on a pistol barrel.  I have a pair of calipers i will check what it is.  It certainly didn't look any larger than i have seen on any otter rifle (should it)  I will measure it and report back

I've seen Colt at ~.065" and RRA ~.100" and they were both 16" barrels, I guess I'm saying I don't know the answer

I'm getting about .072...seems like that could be the culprit here

Ask Adams what size the port needs to be to run their piston?

if you have a 7.5 inch barrel with a .072 port then you should be getting more than enough gas to operate our piston system, even with a heavy buffer. depending on how your barrels gas port was drilled, a measurement taken at the top with a set of calipers could be very inaccurate. i would see if you can measure with a drop gauge or contact the manufacturer to see if they can tell you the port size, before you cut your proprietary spring.    


Aro
Adams Arms Special Projects Armorer

I don't have an AA but that's some badass CS right there.

Before you narrow to the stock did it, did you try:
Another mag?
Mag with one round to ensure proper lock up?
Did you ensure the gas block is indexed to the gas port?  some barrels are out of spec and have the shoulder too far back (I chased this on a build)

Fatkid

How many rounds and of what type have you run through it?

My 7.5" piston AA upper (pistol build) short stroked like crazy with any and all steel cased ammo for the first 500 or so rounds... It ate brass cases ammo just fine (factory and reload).
Either the steel case was sticking in the chamber slightly, or it was just underpowered cheap ammo.

Either way, my 7.5" pistol eats anything now, just needed a good break in.