Failure to chamber round

Hello all. Went to range today to try out DIY trigger job. Loaded up as normal, racked slide to load round, fired, and slide came back like on last round. But next round sitting low on ramp, but not going into chamber. Thought it was just me not shooting for 3 or 4 weeks, and maybe limp wristing. So I change mags, same result. But now, it will cycle 6 or 7 rounds, and then the same problem. Even tried 1 mag with WWB, and 1 with UMC, same thing. Any ideas ???? Thanks.