Superformance powder and the .257 Ackley Improved

[MT Pockets]

I am new to the .257 AI but have always wanted one. I now have mine built on a short action Remington model 7. It ports a No. 1 contour fast twist 20" barrel. I have fireformed new Nosler brass during my barrel break-in and am pleased with the accuracy but now want to load for this upcoming deer season. I selected a Speer 120gr. BTSP and IMR 4831 powder to start. I have less on hand than I had thought after fireforming and am curious as to Hogdon Superformance powder getting me in the velocity range I would like. I have no experience with this powder and hope someone here might and with .257AI experience would be a big plus.

 

[salmonchaser]

No experience yet but planning on sending off one of my #1 in 257 roberts for a new 257AI barrel. Will be following along.

 

[Dr. Vette]

I'll throw in some info on a similar-but-different cartridge.

I'm trying 140 Fusion in my 6.5 CM. The Superformance did not give me the accuracy I wanted at all, no matter what I tried.
I then swapped to StaBall 6.5 and it became incredibly accurate and I gained speed. I was shocked at the difference.

Personally I have not had great luck with the Superformance powder for any loading or cartridge so far.