Not trying to sidetrack the thread, but thought I'd suggest an alternative to a stock for someone wanting to go the brace route. I really like these SB Tactical SBT-G2 braces. You can buy just the brace, without the folding adapter, for stupid cheap at Modern Warrior. Then you just pair it up with whatever adapter you want (Stribog and AP5 below).
Neither of these guns would stabilize Federal 150gr Syntech. A call to Federal and replacement 147gr Gold Medal Match fixed that issue. In the future I need to put a tri-lug on the TiRant9M, it would look better and be shorter too. The threads are too long on both guns for my suppressors (Sig SRD45X, AAC TiRant9m), so I'm using a SilencerCo spacer on the AP5 and the Sig can has a modified piston (same previous issue with PSA AK-V, long muzzle threads).
This is at 25 yards, 147 GMM, on a bench and rest. I've only shot the guns a few times. The Stribog has a significantly better trigger (like a good AR trigger), but with practice I think I could get the AP5 to group a little better.