Re: Russian rifle question
The main difference is the receiver. The M76 has a milled receiver where the PSL has a stamped receiver. Unless your going to work up hand loads your going to be limited to older surplus ammo. If you go with the PSL look for surplus 7N1 ammo, it's usually pretty accurate. If you go with the 8mm look for Yugo M75 ammo. Or if you reload just work up a load on some Remington brass for the 8mm, or you can even get Lapua brass for the 7.62x54r. I don't know if I would use Lapua in a semi auto though, may be overkill and it could tear up the brass.
Ballistically they are going to be pretty close. They shoot about the same bullet weight, though the 8mm will do it with a little less powder. A lot of folks tend to favor the 7.62x54r for accuracy, but then the M76 has the milled receiver. Which is going to make the rifle much more stable of a platform, i.e. no receiver flexing, tighter tolerances, etc.
I've shot both with the same results, about 2.25"-2.5" groups consistently at 100 yds. They are a decent semi auto for a DMR role. With the current offering of .308 ARs and M1As they have basically become more of a collectors item than a shooter. Not knocking them, plenty of folks and soldiers have fielded them with decent results.
Hope this helps out, good luck!