Aim for the belt, depress button for whatever time it takes to spit out 2-4 rounds, repeat until you or the target is dead.Show me a video of someone doing it and I will belive you.
I'd say most of my PPSH kills are from 70+ meters with 100+ being fairly common at least on spartanovka. This only applies to targets in the open though. Nailing a helmet is harder.
Basically never use full auto.
You might also want to level that weapon as recoil and everything else drops a percentage point or so as you level. Either that helped me some or I've just started to "get" the weapon. I do have significant problems in the very short range hitting anything with hip shots but that is the hitreg being iffy. I also can't hit anything really close by if I just spray even with ironsights. Don't know why, my eyes tell me the sights are on the target most of the time.