[I can't remember if I posted about this before...]
Over on another forum someone from here talked about his idea of cutting up a Mosin Nagant rifle receiver to destroy it, then rewelding it to create a brand-new "pistol" receiver.
He got dogpiled and the thread disintegrated, but the idea stuck in my head. When a 91/30 barreled receiver showed up on Gunbroker for $19.95, well...
I'd never taken my Mosin apart, so looking at the receiver was interesting. The Mosin bolt rides vertically, guided by the bolt handle riding the slot on top. It turns horizontal to lock, like a Ross straight-pull action. Or vice-versa, since it predates the Ross.
What this means is there are no 'raceways' down the inside of the receiver like a Mauser. Instead, there's only a short section right behind the barrel threads.
The Mosin receiver starts as a piece of bar stock, with everything that doesn't look like a receiver cut away. But other than some of the trigger and stock mount bits, it's close enough to a tube. If you were building a pistol you wouldn't care about the stock mount bits anyway, and you could fab the trigger housing bits from sheet metal.
The short raceway sections at the front could be done with an end mill and a file, or even just a file and patience. Then you'd have a 100% scratchbuilt receiver.
You'd need a lathe and a mill. It would be more work than a sheet metal AK receiver, a whole lot less than a milled AK receiver or a Mauser receiver. Probably about the same as doing a 0% AR forging.
The reweld idea still looks interesting, particularly if you take two different receivers and use the front of one and the rear of the other. However, the ATF hasn't (as far as I can tell) made a ruling on what constitutes "destruction" of a Mosin receiver. On atf.gov there are drawings of various rifle receivers showing where they have to be cut, but the Mosin isn't one of those. I've been meaning to write the ATF and see if I could get a clarification; I guess I need to get off my butt and do it.