Slightly oversized workd for me.
As said above I use a 6MM for my AR-15, a 7MM for my 6.5Sweds, an 8MM for my M-1 Garand and a 338 on my 8MM . BUT, AND I THINK THIS IS IMPORTANT. I ALWAYS soak the top--up to and inckuding the brissles with KANO-KROIL. and pull up thru the Breach end holding the muzzle down and standing on the rope( string). It's a little tight but it works for me. That said back in the Corps after shooting our M-1 garands we would field strip them, take the Barrel/receiver over to the Mess-Hall get the steam hose, stuff it in the chamber end, let it blow around 15 minutes then oil it down. Never got gigged during Rifle inspection by the Gunny