Recoil? I have a Thompson Contender in 7:30 Waters. Nothing to it, holding it with no stock at all, pistol grip. Barrel slightly longer than this. Also very accurate. They make their current handguns in 308 and 30-06.
Probably a lot less than you expect, the short barrel isn't going to allow for a lot of pressure push back.
As for the gun in question, could have been a one off, not something commonly done.