This post is for about 7 people in the US as dumb as me to want to SBR a P250 module to shoot 22lr in a B&T USW-320 frame and then realize like $1200 into it that the mags only come in a compact and don't fit.

Two solutions:

Plan A) Get the Dremel and go HAM on the $350 grip module

or

Plan B) Make a 3D printed magazine extension and a jig for drilling a retention hole. The existing baseplate snaps on to a small protrusion and fits tightly. You'll need to source a 1/8th in pin (nail, roll pin, whatever, cut to fit), and drill each mag using the jig. A little filing maybe depending on your print settings, and the pin hole is undersized so you can get a nice tight fit on the mag.

I figure I put enough time into making this work that someone else in this spot might benefit, so here is the final product free for printing. And likely someone will post a "Some guy makes those on ebay" but anyway I had a good time making it. As a plus, it increases the capacity to 12.


Couple of different places to download a copy of the STL files to roll your own if you need it, I hope they are shared correctly:
https://thangs.com/Jt526/P250-...zine-Extension-34591
https://www.thingiverse.com/thing:5089939
https://www.thingiverse.com/thing:5079600

The reason of all this with an extended mag in:


Mag with extension installed, mag with extension top profile and extension side profile




The problem and solution with mag too short in magwell and extension shown next to another mag:


The jig in a mini-mill: