.020 over caliber size is the magic number. I have had two breaks on my 260 and am really thinking it is a waste. Breaks seem to work better the bigger the cartridge is. Saying all this; I have a friend that has a AR10 with a break and with that platform the rifle has zero recoil it dose not move off the target at 100 yards. On a 6 I think you'll find little benefit from a break, let alone one that is way oversized. If you already have a 6 that is threaded then I'd try it. Nothing ventured nothing gained, is what they say.