I figured if 4.7 with a fmj does 1150 dropping down to 4.5 grs should keep it under the 1250 mark and with such a fast powder the extra inch on the barrel shouldn't add as much extra velocity as others I use like autocomp and sr4756. I wouldn't even flirt with any type of crimp but I don't see the need for it either. I really need a chronograph. I do wonder if they guarantee them to 1250 I wonder how hard you could run them before they start to come apart.