I'll state what my thinking was when I got my Harvester 30 can a few years. I only wanted one can for all of my CF rifles, and a range buddy and the shop owner confirmed that I could use the 30 cal can on everything up to a 308 caliber with no ill effects on performance or accuracy. Largest caliber I have/shoot is a 6BR, so I just got ONE 5/8-24 threaded end cap for attaching to the muzzles, and all of my barrels are threaded the same 5/8-24. I don't change the exit end cap for any caliber I shoot (20 cal up to 6BR) , I just screw the can on to the gun I want, and shoot. I just have to adjust/re-zero the scope due to the can. When I don't use the can, I usually have a muzzle brake on to annoy the 338L guys who use a brake at the range, or anyone else who uses a brake on the larger calibers.