I was going to start a new thread about things to look for on a new, out of the box s2k, but this might be the proper place.
I haven’t seen anyone mention these two things, and im not sure how common they are, but they were both an issue on my gen2 40.
The first. When sighted in, the front sight pin was far left of center, due to the front sight not being properly aligned straight up on the barrel.
The second. The fore stock had a tiny bit of play if you held the rear grip and then turned the fore stock back and forth. It wasn’t much but it was there. It would certainly have affected any scope and problems with the ability of a folding scope mount to re zero consistently.
I loosened the front nut and set screw, straightened the front sight and re-tightened everything. then the sight pin was centered when re-sighted.
I took the fore-stock off and very lightly sanded both halves so they came together tight on the barrel, before tightening against each other leaving a tiny bit of play.
BE VERY CAREFUL IF YOU DO THIS AND BE SURE TO SAND BOTH HALVES EQUALLY!!!
It doesn’t take much. I did mine very lightly, put it back on, replaced and tightened all bolts and checked it.
It needed just a tiny bit more to be solid so I pulled it and did just a little more. Rock solid after that.