My .257 AckImp delivered exceptional accuracy from it's 26" Shilen barrel using bullets from 75gr. to 120gr. It was a 10" twist.
75gr. Hornady HP - 3,950fps
87gr. Hornady SP - 3,650fps
100gr. Nosler Par - 3,484fps
120gr. Hornady HP- 3,219fps

I most certainly thought the AckImp was worth it. While I had that gun, I chrono'd a fellow's rifle, who just had a .257 WTBY made up on a BRNO action. His seems to be a slow barrel, as it was over max using IMR4350 and 100gr. Noslers at 3,482fps - he needed to use a piece of 2x4 to open the bolt, yet his load was straight from a book - at 68gr. 4350, he said. This was in 1978.
Odd I can remember that like it was yesterday, but the fact my little ctg. out-sped his yet used 15gr. less of the same powder, amazed me.