Well,,, the good news is PPU makes ammo for the gun. Best to know many (or should I say most) used M-53's have some degree of cone damage from the intensity of the round. At the entry of the barrel, will be beveled not flat across, noticeable even in photos, good question to ask seller.
I've compared the PPU against Remington's ammo had since the 70's and found PPU's have substantially less power, hence less apt to burn out that cone area.
Mine came with the extra .22 LR cylinder and is super accurate in that configuration, not near as well with in Jet though. The casing can get stuck in the camber, I bring along a simple hand tool I made,, when won't eject all six at once do them one at a time with the tool, simple.
First photos the M-53.. Have basically the full S&W line, my M-48 and M-53 .22 mags use the least.