Just becuase the back end of a target isn't all blown out like a .30 rifle round just does not mean there is a clean .30 cal hole through and through. A round going that fast (Specially at smg velocities around 2200fps) it's going to leave a CONSIDERABLE wound channel through soft tissue, not to mention extreme fragmentation of bone if one was in its path.
At least from an SMG you're talking very similar muzzle energies to 5.56 in a 16" carbine.
I've seen the figure of 1800 FPS quoted for the 7.62X25 post WW2 SMG loadings, a more powerful round than that used during WW2.
The same SMG load was quoted as traveling at 1500-1600 FPS from a handgun.
Every site I can find quotes muzzle velocity of the PPSH as 1600 FPS, which sounds right for the standard pistol loading fired from the longer barrel of the SMG.
A couple of years ago I ran across a site with X-rays of a 7.62X25 Steel Core milspec bullet buried deeply in a victims ankle. It was a pretty badly messed up ankle , but not shattered as you might expect.
The X-rays came from a police shooting scrape, not sure who shot who, but apparently the Tokarev is still in use by some former Soviet Bloc police.
Even at 1800 FPS from an SMG the 7.62X25 would have somewhat less energy than the M-1 Carbine.
IIRC the 1800 FPS SMG load was developed to counter U S body armor of the Korean War era.
The PPSH with the early ammunition could penetrate most flak jackets and helmets at close range, but not always at longer ranges.