Tecno,

Have you considered a .256 Mannlicher (6.5x53R Dutch). There have been some very fine double rifles made in this caliber. Great penetration with the 6.5mm bullet as it has a very high SD for the heavier weights. Brass is easily formed from .303 British. Dies are no problem. You can shoot light weight bullets all the way up to the 160gr pills. Worth investigation.

Good luck with your project.

Corbin