I've messed with them, from .25BR, up to .25/.300WSM (.257 IdiotMag) - my favorites have been .257 Roberts, Ackley Improved. In 2013 & 14, won yardages (a pair of 200Yd.) and Grand Agg. NBRSA Hunter Nationals, with a Bartlein (1:9" twist 4 groove) barrel chambered for the 25x47 LAPUA. .257s are GREAT performers!
The .257 IdiotMag was "designed" - ordered as soon as the case was SAAMI spec'd - simply a necked-down .300WSM - with 110 Gr. BT, it delivers 3520FPS with sub 0.4MOA grouping, and of course, is a great mule deer killer. The .257 Ack. Imp. runs the 110s at 3330 FPS (Rl-17) and has been deadly on mule deer too!


RG