Or I may ask what would be the bore size of a 7.62 silencer?
Normally suppressors and muzzle brakes are bored .020 over, or a 7.62 (.308) would be .328.
I tad bit bigger wouldn't hurt. I'd still bore it instead of drilling it if it was me, but .375 (3/8) would work.
Instead of drilling, and if you don't want to bore it, ever thought of using a reamer, they make cleaner, more precision holes.