I'm looking to build a SBR. We're an 07/02 so we can go ahead with the work at will, but we're unsure what barrel length is best with what twist rates, etc... I'm thinking a 10.5" barrel is what we want, but if the collective thinks we can go with shorter (8.5" maybe) we would probably do that. My questions are this: What would be the best twist rate in 5.56/223 for a 10.5 and 8.5" barrel? What would be the best twist rate in a 300blackout in the 10.5 and 8.5" barrels. and finally, is the 8.5" barrel in either caliber going to be so short it kills velocity and affects accuracy because of it? Thanks all.