- 300rds SS198LF - 200 through the PS90, 100 through the FsN
300rds American Eagle 40gr - 200 through the PS90, 100 through the FsN
50rds of R&R Weapon System R37.X - all 50 through the FsN
Save for the first magazine through the PS90, which had 3 failures all due to the American Eagle ammo (all with a non-trivial amount of bullet setback!), it ran flawlessly. The groups at 25y were ~2in and it was amazing to shoot. This is easily my favorite rifle now; it's accurate, low recoil, high capacity, lightweight, and looks fantastic. A real joy to shoot and own.
The FsN experienced only 3 FTF's and ALL were [disappointingly] from the R37.X ammo. It shot up the American Eagle and SS198LF without drama, but on 3 occasions in 50 rounds, the R37.X ammo would "stick" half-way in the magazine, as though hung up on the rim, and fail to chamber. Very disappointing, as the cost was non-trivial for that ammo, it's ballistic performance was exceptional in Buffman's videos, and I have 100 more of the stuff that I'll likely not carry now. I will say this: you can tell it's loaded hot - it has a lot more blast / noise than SS198LF or AE 40gr.
I have ordered ~ $500 worth of EA's T6B, which I'm really excited to try out, but that hasn't arrived yet.
For the sake of reference, I also brought along my Sig Sauer P229 Legion in .357Sig and P226 Mk 25 in 9mm - after shooting all of the 5.7 up I switch to those. It's odd to say, but 9mm just "feels slow" after shooting 5.7. Both 357 Sig and 9mm have more recoil, but less bark - particularly compared to the R37.X. The .357 Sig was close in report, but not quite as sharp. Another quick observation while I'm thinking about it: that barrel on the PS90 gets super hot; steam rolling off of it after 100rds - natures way of saying "do not touch." It seems to get hotter after 50rds than my AR after 200rds!
I'll report back after I've tested out the EA T6B - really looking forward to that as I anticipate making it my carry ammo