The Browning Hi-Power magazine has two floor plates:
- the interior plate captures the spring and locates it properly inside the magazine case
- the exterior plate provides reaction force against the spring and locates the interior plate’s boss
The interior plate has two critical features:
- the ramp on the front (to the right) that guides it over the edge of the exterior plate
- the boss that latches the exterior plate in place
If you remove the interior plate, you must somehow hold the spring in place while sliding the exterior plate in place, after which the spring is free to thrash around inside the magazine under recoil forces.
An important point: you can buy exterior floor plates from all the usual sources, but, as nearly as I can tell, nobody sells replacement interior floor plates and they’re not included in kits of replacement springs. If you don’t have an interior floor plate, you must fabricate one from scratch before you can use the magazine.
So one thought is to drill a hole in the middle of the boss:
OK, that’s not quite centered, but it’ll suffice.
Wire-brush the coating around the inside of the boss to prepare it for brazing, then braze a nut onto the inside of the floor plate (which I haven’t done yet), and run a socket-head setscrew through it:
If that threaded into a block loaded with steel-filled epoxy, it’d never come back out again. You could machine the head down to a flat disk that would fit through the existing hole in the exterior floor plate and not provide any gripping surface:
To be absolutely certain, you could file the entire socket head off flush with the boss, leaving no way to grip the screw.
If the block surrounds the nut on the floor plate with a generous helping of steel-filled epoxy, then there’s no way to twist the block off the plate.
If the block also captures the spring, then you can’t heat the plate enough to un-braze the nut without also de-tempering and wrecking the spring.
I can think of a few other ways to attack it, but none seem like a project that would readily convert the magazine into one holding a few more rounds. Opinions may differ, of course, but …