At least some of POA's loading data for the 257AI is very hot, far exceeding any currently recommended loads. I remember a member claiming 257 BEE performance from a 257AI with loads that he got from data that Ackley published. IIRC, he hadn't run any of the loads over a chronograph, so he really didn't know what they were doing, but because POA said so, it was so, at least in his mind.
I had a Ruger #1 in 257 Roberts awhile back, around 2003 or 2004. I understand that the guy who I sold it to had it rechambered to 25-06 in order to eliminate or reduce the freebore jump to the rifling that it came with.
Never looked and compared the Bob, data, but the POA published load data for the .250 is close to what Sierra listed on their # 5 load manual at least for the 100 grain bullet. For that 100 gr bullet, I believe they are within .5 grain for 4064 close to that for the 4350 powder as well.
For me, my M99 250 AI shows the best results with RL15 and H-380 powders, but both are on the lower side of the AI "improvement" gains. Anything close to the mid-higher range in speed/powder as shown in the Sierra book and I start cratering primers and having lever opening issues. I might try revisiting the 4064 powder again.....
