Trying to get PSA AK104 12.5" to cycle subsonic brown bear 196gr ammo, anyone have any idea where you can get a reduced power recoil spring, or is my only option to clip coils from stock spring.
Thought about drilling out gas port but the PSA AK 104 has a 90 degree gas port so would have to remove front sight/gas block to access port. Even thought about drilling holes in non critical parts of bolt carrier to reduce its mass, but that seams a little drastic.
Any thoughts or ideas would be appreciated.

It is going to be difficult to titrate the right balance to cycle subsonic without a suppressor and also run supers (assume you still want to do that) without being way over gassed.

Have you tried running the sub sonic rounds suppressed to see if it cycles and be happy with it cycling only when you run subs suppressed?

The most practical way to get it to run widest assortment of loads is the port and open it up then choke it off to correct gas setting for the round - problem is not too many options for AK gas blocks.  Some have done a DIY gas block by drilling and tapping into the block from the font, and and using a set screw to choke off gas.  You would have to open the port wider than it is and then choke it off for the load.

Definitive arms makes a gas block several types.



ETA - This might sound odd, but maybe others have tried - There are several vent notches on your gas block on the rear - these notches vent excessive gas to reduce powder in the action and slow the action down a little.  I onder if they were covered up somehow if it would run with subs.

Un-suppressed won't cycle enough to eject, suppressed will eject but not cycle enough to chamber subsequent round, and yes I was eyeing the gas relief ports around the gas block/ tube interface and had thought about making an adjustable collar to close off the ports for subs

I read somewhere that particular load was designed around functioning with a 16 inch barrel, and shorter barrels either won’t work, or will take lots of modification to get to work.

I thing I'm going to try and roll my own with .308 220gr berry's and some Blackout sub powder like AA1680 or some thing, been trying to find out if PSA actually uses Com spec .310-.312 groove or standard US spec .308 barrel blanks for their builds, either way I'll give the 220's a shot

Use a silencer. No point in shooting subs without one.

Probable should have mentioned that in my first post, Un-suppressed will not cycle at all, Suppressed it will cycle to the point of ejecting the fired case but not enough to pick up a fresh round, could clip recoil spring enough to get it to cycle but then it probably won't have enough spring power to strip the next round.

I wouldn't clip the spring, needs a slightly larger gas port and KNS piston for going back to supers.

Sometimes shooting suppressed is like this:



On shorter barrels you don't have the dwell time to have better back pressure.  On 300 blackout AR15s this is why they push the gas tube further back closer to the chamber on shorter barrels.  

I’d get an extra spring and try shortening it in small increments to see if it could work. If so, you could set up a complete extra spring guide assembly to quickly swap back and forth.

I’d modify the least expensive part first.

I did the clip the spring one coil at a time til it started ejecting rounds consistently. But it was having issues chambering rounds once in a while. I changed magazines, everything started working. Seems as though mine had problems stripping from steel,magazines. Switched to Bulgarian, AC Unity and East German Bakelite, started working great.