Every ar is different, don't be afraid to experiment. A few variables come into play, each typically minor, but add those variables together and your firearm gets a unique personality. Gas tube length, buffer spring, weight/smoothness of bcg, the efficiency of the entire gas system, ammo.....I usually start with an H2 (apx. 4.6oz), seems to work well for me. I really like the spikes t2, slightly lighter than an H2, but uses powder instead of solid weights. It feels smoother to me, but that idea could have been planted in my head from the product description. either way, im happy with it. I haven't owned a rifle length so I can't give much input there (standard h buffer maybe?). All that being said, I am interested in trying out one of these buffers as I would prefer to see my money stay in canada given the option...good price too