I've had my S2 orange a few months now and have been shooting it regularly. I happened to be loading 115gr jacketed RN with Unique when I bought the gun, and the gun would lock open when empty with that load. I was just looking to use up the last of the Unique I had, which I did recently. Went back to some tried and true Win 231 loads and even at the max load, the slide won't lock back. Tried some factory 115gr range ammo too (blazer, white box and herters). None will lock the slide open. All of the above loads lock the slides open on my Sig X5, P229 and P320's.
So I figured recoil springs. The orange comes with 2 extra, but same problem with any of the springs. Ordered the CGW "white" 10lb spring. Really thought that would do it, but no joy. I clean the gun after every other range trip. Stock firing pin/spring. Stock trigger return spring (although I have the CGW lighter one on the bench). I did put a lighter hammer spring in, one of the ones that came with the gun.
Is this just a thing with the S2? I do not want to shoot Unique long term. Dirty powder. And at 5.7gr, the case is full enough that I have to slow down my reloading so it does not spill.