Hello Al!
We recommend our VihtaVouri N565 High-Energy powder for your safe consideration for your .257 Ackley Improved cartridge...
Recipients of load data and/or product technical support from Capstone Precision Group LLC, assume all risk, responsibility, and liability for any injuries (including death), losses or damage to persons or property (including consequential damages), arising from the use of any load data or product, whether occasioned by seller's negligence or not. Capstone Precision Group LLC, neither assumes nor authorizes any person to assume liability in connection with the use of any data or product provided.
Always begin load development by using the minimum load data and approach maximum load data with extreme caution, as all rifles and reloading techniques differ. CAUTION: If you substitute or change any components (including lot numbers for different powder, brass, bullets, and/or primers), you must restart the load development process by returning to the minimum published load.
The 6.5mm calibers features in the Berger Reloadng Manual 1st Edition are:
6.5 Grendel
6.5 Creedmoor
260 Remington
6.5x55mm Swedish Mauser
6.5mm Remington Magnum
6.5x47mm Lapua
6.5-284 Norma
6.5mm-06
264 Winchester Magnum