If you look around here many claim the latter backup with the firing pin safety always had more problems than the one that does not.
That being said I found a NIB backup without the FP safety and messed with it for awhile and failed to get it anywhere close to self defense reliable.
I changed the recoil spring and smoothed out all the elements that were rough from the factory and still no-go.
Turning towards the mags I had 5 mags to play with and I noticed that the follower on the AMT mag is really floppy at the front end, I tried modifying the mags going so far as to try the follower from an ed brown mag that offers more support / stabilization and stronger mag springs. Ultimately this lead to a 4 round mag that was almost reliable. But not quite. I considered brazing a catch to the back of a wilson officers mag and seeing if that helped but I gave up.
I'd rather stuff a J frame in my pocket among other things than the AMT all things considered. I'm not mad, I went in with eyes open and learned a whole ton in the process.
Ed Brown does not build less than a commander sized 1911, he says it will not be reliable. Others do but many of the reports here of 1911's with issues come from the officer sized 1911's. Likewise many of the micro 9mm / 380 guns have issues that need to be ironed out. I am not saying AMT is bad, but I will say that any small for the caliber auto needs more attention to detail and I do not see that in the AMT.