I have a 257 AI that I built from a 98 Mauser action.
I get close to 25-06 velosity
I would shoot the rifle before it is rechambered ,a poor shooting 257 Roberts will be a poor shooting 257 AI
I now load Swift 120 gr A- frame bullets ( dealer sold them at cost ,someone ordered them and never picked them up) with IMR 4350
I have used the Nosler 115 gr BT ,with great results
This year 2 , 1 shot kills on deer 150 and 225 yds
In the spring it becomes my heavey varmit gun with 85 gr Nosler BT's
Best of luck and post results