First, try letting the barrel really cool off between shots. If that doesn't work, make double sure you have the mount, rings, and scope locked down. I put loc-tite on the under side of the mount, and on the screw threads. I also put a thin film of it on the bottom of the inside of the scope rings. Once that sets up, you should be able to guarantee the scope doesn't move.

I got a Rossi in 7.62x39 for my son. It shoots fine. Not a sub-MOA rifle by any means, but plenty accurate to kill deer. The factory sights on it sucked.