I`m going to build a 308 with 18.5" barrel. That way it will be around 20" at end of brake. I am going to shoot either 155gr Bergers or 155gr Lapua Scenar bullets. Since my velocity will be on slow side, I was wondering what twist to go with? After doing some research but nothing really found, I believe 12 twist since my velocity will be close to that of a 300 Savage and thats the twist that cartridge has. Any help will be appreciated.