I have my parts list together for a 500yrd and closer TC prohunter pistol. Encore frame, full spring upgrade kit with 2# trigger spring. M4 rilfe foreend. Harris canting 6" bipod. Flex tec pistol grip. 2.5-8x28 Nikon bdc. Custom 6 hole base with matching rings. So here is the question, I am going to have MGM make a custom barrel, 18.5" long so it finishes at 20" with the brake installed, so out of the cartridges I list and someones experience I would like opinions on which one is the most effective and efficient, I don't want a cloud of unburned powder coming out the brake, so here goes. 7mm-08 120grn NBTs with Varget 284win 140 vlds H4350 243win 87grn vld Varget or 4064 6.5x284 123 amaxs Imr4350 260 123 amax Imr4350 Last odd ball option, 30x284win 168 NBTs 4064 I will greatly appreciate any input from you long range pistol shooters, thanks.