Hi all hope someone can help. I purchased a c96 swedish mauser supposedly in 303/25. However it wasnt it was 303/25 rimless. The old procedure for making these cartridges was to grind off the rim of a 303 and then grind in a groove to make it rimless. Then also neck down to 250. That is too hard so i scoured the the case data and noted that 220 swift is virtually identical to 303/25 rimless just needs to be necked up. So after annealing and necking up in two steps it worked well. My problem lies in the fire forming. I started with a 100 grain projectile in front off 36 grains of 2208 and the result was case head seperation as the case wants to bulge (about 12 thousands) to fit the chamber. I think my load was too hot and that fireforming to meet the chamber was too violent. I note that the necks and shoulders were still perfect and 220 swift being a solid case should be able to take the fireforming. So can anyone suggest a procedure or gentle load to fire form the brass.