16rd 'B' Mags came in from CDNN today. The mags would seat to within about 1/2" before they would stop. I stripped it down to the frame so I wouldn't accidentally file the ejector block and started fitting.
I was about to break out the dykem to mark everything and see what was binding, but with the grips off I could see first off that rear magwell opening part of the backstrap was causing the mag to tilt forward slightly the more I tried to seat it. I filed with a needle file for a couple dozen strokes and VOILA!!! the mag would seat flush.
When pushing the mag release though, I had to strip the mag out. I then looked at the upper rear portion of the frame inside the magwell and filed on the entire flat portion that is just below the trigger bar.
Reinserted the 'B' mag and hit the mag release and it dropped right out!!! Cleaned everything and touched it up with a little bit of cold blue....reassembled and function tested. Everything works great.
If you are going to try this, go slow and test fit so you don't take too much off.