Originally Posted by 9mm +p+
Or just find a used Gen 3, I wouldn't take a gen 4 if it was free.
or this as well, anything with an L or earlier serial is safe, maybe M, N and possibly O as well.
M&P 40 CORE, M&P FS 40, M&P 40c, M&P 40 Shield
DDM4V1 LW, DDM4V5 LW, SCAR 17s, VEPR 12