Not Sierras, but I have shot Nosler 77gr match out of a 20 inch bull barrel AR-15 with 1:9 twist and it shot clover leaf groups at 100yds with the standard load of 24.5gr Varget and bullet seated out to within .002 of the lands. Sierras would probably work as well. You just have to shove them out the snout as fast as you can without getting any pressure signs.