If you reload for your m&p 15 its 16" barrel makes very little use of all the slower powders like varget, cfe223, reloader 15 and theres alot more but I have always heard shorter barrel faster powder well ive used alot of different powders imr8208xbr is my favorite but I decided to try some 3031 I had just to try the old saying bout short barrels well its true of course im above book max listed but absolutly no pressure signs at all ill give bullet and velocity 65gr. Game king 2,858 fps and 77gr. Nosler c.c. 2,630 fps thats out of my m&p 15t I did work up all loads and shot them in 87deg. Temps wjth high humidity and let the rounds lay in the sun for bout 15 min. Just to chk for pressure signs there is none the brass was not stretched either tried to trim after sizing none touched the trimmer and as far as accuracy goes with the 65 gamekings 5 shot group at 100yds center to center measured 0.397 and the 77gr. Noslers were 1.5" at 100yds and surprising 1.5" at 200yds I was using my lead slead solo to help eliminate alot of my errors this is my first post now 8208 did give slightly faster velocity with the 77s but accuracy was 2 1/8" at 100 yds and it could not match velocity and accuracy with the 65s without showing pressure signs so I ussed winchester brass , wsr primers for the 65gr. Load and federal brass, ccibr4 primers for the 77gr. Load and of course imr 3031powder I dont mind compressed loads 
