How difficut would it be to do this conversion? Could you use the stock barrel or would the chamber be too long? Magazines? You should be able to get some really impressive velocities out of a 12" barrel.
It would need to be blowback, not sure if there is a gas-assist 7.62x25 barrel.
Basically like the Bizon conversion, sans the tube magazine. Or Rhino's .45 conversion. You'll need a PPSH barrel *OR* any barrel in 7.62x25 for that matter, and a lathe to turn the journal down to 23mm. I say "any" barrel because in theory for a pistol you could use something like a CZ-52 barrel, lathe it down and sleeve it to fit.
I'd opt for a .357 SIG on a 1911 frame before I went w/ that caliber. In fact I just bought my Para Ordnance Warthog (updated P10) in .45 ACP and put a Springfield Armory XD .40 Sub Compact on order. The XD40 can be converted to .357 SIG w/ a barrel replacement which is on my list.
Back to the thread... You could do it either by imitating a Bizon - cut the receiver to move the trunion back to fit the magazine - OR you could use a mag well block to fill in the gap. Sleeve a barrel, keep all the original parts, and there you go.
That very thing is what I have on the plate - a Bizon conversion in 7.62x25, immediately following my 9mm conversion. That's one of the calibers that I have read the Bizon comes in. I have a few pics of the Bizon using PPSH mags, and AFAIK they are interchangeable - both the Bizon drum and the PPSH stick mags in that particular caliber. Or maybe there's a mag well adapter, not sure.
Instead of putting a mag well block on a normal AK frame, I'm going the cut-frame look of the Bizon. It is important to me that it uses the stick mags as well as the drum mag, so I'm awaiting the PPSH barrel and magazines before I can fit them up. But that's all after the 9mm conversion. Using Suomi stick mags for it.