The barrel is threaded for a screw-on muzzle device of some kind, most likely a suppressor, or a fake one anyway. The end piece that screws onto the barrel protects the threads from damage when the device is not on the barrel.
The ammo is a mystery. It looks like caliber 7.62 x 25, but I never heard of that pistol being chambered in that caliber. It also wouldn't make any sense to use a suppressor with that caliber, as it's a powerful round and would'nt be muffled very much, I suspect. It would make much more sense to suppress the .32 round. I wouldn't try to fire that ammo until you're SURE it is for that barrel/pistol. I wouldn't fire it at all, actually; I'm not sure the pistol could safely handle it.
It any event, you have a very interesting piece that I'm sure has a colorful history.
Any chance you could post photos of all the markings on the pistol and barrels, or at least describe them? It might help identify the pistol and give some clue as to it's history.