After finding this thread months ago, I finally got the mags needed to try it. It took a while, but I used a new Savage 55230 mag and a ten round m3 Pmag to make mine. I cut the feed lips off of the Pmag at the mold line and it fit nicely against the step in the Savage mag. Drilled holes through the rectangles into the pmag and found finishing nails to fit with a little friction. Cut the nails to guessed length and ground down the heads flush with the metal body. Trimming the follower was pretty simple and no spring cutting needed. My biggest challenge was getting the hollowed out floor plate back on the Savage body. I ended up grinding half of the tabs in the old floor plate and easing it into place. The rear of the Pmag follower hit the Savage spacer and needed to be filed to feed past 5. Cycled all 15 twice, but haven't fired with it yet.

It's solid, but I doubt it will hold up to many drops. The next one I make will be all metal and welded.

I also wanted to thank you for sharing this idea. It was a fun project.