It shoots anything I run in it. I suppose if you tried lower pressure ammo from the start (before breaking in springs) and/or didn't have your bolt generously lubed you could have issues, bu I haven't.
My default ammo though are the Federal 9BPLE -- a +P+ HP load -- and S&B SB9A FMJ. Both run hot. The S&B is essentially a 9mm nato pressure load but w/ a 115 gr bullet rather than 124.
SB9A is listed at ~150 fps faster (1280fps vs 1090-1145 fps) than federal fmj (standard pressure, american eagle is loaded w/ less pressure than is redbox) and the federal 9bple is listed at ~120 fps faster than standard pressure federal HP loadings for the Federal 9BP (that's at 1180 fps, vs 1300 fps for the 9bple).
*I shoot these for velocity gains/flatter shooting not out of necessity for function. And I haven't tried steel or aluminum cases in it either (believe the manual says to avoid aluminum).
I like it enough that I'm planning to pick up a second to keep in my wife's car as a trunk gun. And I went w/ Glock b/c their high capacity mags (33 rounders) were the most reliable out there.
However, the Sub2k does have its own specific manual of arms. For me, the compactness gain was worth it. Depending on what you/yours run or are familiar with, a Colt 9mm or Citadel 9mm M1 Carbine clone might make more sense (Citadel uses Beretta 92 mags). Those are the three 9mm carbine platforms I'd consider/recommend (I'd classify an IMI or Action Arms Uzi as a SMG rather than a carbine, but it's a fourth option as well -- and my first and only choice for SHTF situation if I had to pick just one but that's not my use case here, well maybe the Colt just due to accessory options...). Regardless, other options all have major drawbacks: the Taurus if there were conversion packages available, the Suomi if it didn't weight so much and was reliable with all ammo and if the conversion kept more of the original operating system, the Beretta 9mm carbine if its hammer and other integral parts weren't polymer [+$200-300 to replace those which brings to colt 9mm price range], Marlin Camp if they weren't relatively fragile upon part failure, Ruger is heavy with bad trigger pull and no current production mags, and the HiPoint has the same propriety just standard capacity mag drawback...
