I am in the process of sorting a rifle for a freind for longer shots at small animals, he currently has a std SPS varmint 22-250 that has been Ackley improved, 1:14 twist so didn't try the heavy pills but had the 55gr pills in .274 @ 100 doing 3750fps....at 3950fps it didn't group as well and a little close to preasure, Great round but he is converting all his rifles to LH so has another to LH rig to rebarrel but still tosing up between 22-250AI again or 243AI faster twist as my 1:10 wont stabalise the 105amax (As I shoot that so have the dies for both) If the mag was longer would love to do 6mm rem AI as with its long neck seals the gases well

(also shoot a 6.5-6mm Rem AI )
If you do go longer barrels you need the larger profile to keep wip under controll.......6mm BR is an efficent killer and you dont get too much extra for a longer barrel so if you want a shorter rig its a handy cal