Thread: 7x57 Ackley

Jaco, before you start spending think about what you want to achieve, my experience with the 7x57 is that it will not deliver more velocity with 140 - 160 gn weight projectiles when loaded hot than a 708. I had a mauser and now have a merkel K4 in 7mm.
Going to the improved version give you lots of cool factor but not much increase in case capacity. W760/H414 is the go to powder for velocity and accuracy in the 7x57 mauser.
My .257AI Roberts experience is the improved case will hold about 54-55 gns of 2209. The increased velocities (3300+ fps with a 100gn, 3000 fps with a 120gn) folks get with the improved version of the .257 Roberts are due to loading to higher pressures vs low pressure factory loads for factory .257R. If you load up a std Roberts to similar pressures the gains are 100 - 150 fps, not 300 plus.

I reckon you may need to go to .280 or 7mm RM to get a good improvement over the 708/std 7mm mauser.

If you do go this way have a look for a nice BSA pre CF2 in .243 or .308. These rifles have intermediate length actions, longer that a R700 or sako in the similar calibre and you can fit a x57 AI case with a shallow seated projectile into the magazine. They originally came out in 7mm in this action. I have a Monarch and really like them, they are push feeds. A good one should only set you back $5-600.
Remington build .257 Roberts on their medium 700 actions but they are in reality to short. Mausers obviously work well for the x57 case.

I find that after case forming and running 4-5 high pressure loads my .257AI brass is done. Neck splits and shoulder cracks. Annealing should help this. Fireforming brass is simple and you can just use std calibre loads but it is another task.
Mathias, my old mauser feeds the .257ai ai case well, I may have done some work on the rails though.