[USMC-F4]

This is an example of what the opening will look like when you mill the upper of the USC to take UMP mags. You can use a milling machine or several files or a drill press with X-Y slide or a Dremel and a very steady hand. I did my first UMP conversion with a chainsaw file, razor knife and Dremel. This is my second now that I have a bit more tools in the shed. You can find the dimensions posted on the web.

I'll show the finished product when I get the the 0-1 lower, compliance parts from Adam and do the dye job. Take the plunge, it is an easy conversion.

Cheers!