Last month I replaced the sear housing block on both of my M&Ps. I did it so that I could put a larger sear spring in and fix the problem of sear bounce (dead trigger). This would happen occasionally, especially after reloads.
Well, I got that problem fixed. But I noticed I was still having trouble after some reloads. It wasn't a dead trigger, but two other problems.
On my back up gun the barrel fit is a bit tight and sometimes when I jam in a magazine I will knock the slide slightly out of battery. This was happening because the fit is tight and my recoil spring is light. So I put a slightly heavier recoil spring in (13lbs instead of 11lbs). Unfortunately, that will mess with the feel of the recoil and so won't work for matches. If my primary gun breaks and I ever have to use my back up gun, I'll just switch out the Storm Lake barrel and recoil spring from the first gun.
The other problem I noticed was that after a reload the first round would not camber. The round would not even make it close to the chamber. After testing a bunch of factors I discovered that my magazines were filthy. I had not cleaned them in months and months. There are a couple that I use all the time and they were the source of the problem. So I cleaned them all and made sure my rounds were moving freely into the chamber. I also cleaned the insides with Fire Clean hoping that will help with cleaning in the future.