My Styer SSG will shoot tight groups with the right ammo (it prefers 167 grn, PSPBT at around 2750 fps.) and letting the barrel cool between shots. The only thing I've done to it was a double set trigger, I didn't like the single set trigger it had. Still shoots well for a forty year old rifle.

The rifle shoots better than I do, most rifles shot better than the shooter. My groups may move around the ten ring a little, atmospherics, air temp. ect. But clover leafs are common.

I'm a hunter and the first shot is usually the only one that counts anyway.