The maximum rim dimensions for any commercial loads to be sold in Europe are prescribed by the CIP. According to the CIP tables the rims of the .5x53R Mannlicher are 1.25 mm = .049" max thickness and 13.4mm = .528" dameter, while the .303 British rims are 1.63 mm = .064" thick and 13.72 mm = .540" wide. I never had any problems with the larger rim thickness of reformed .303 brass in 3 Rifles, but I had to reduce the rim diameter slightly to work in my Gibbs Mannlicher. Besides, the cases with the reduced rim diameters move far better through the Dutch and Portuguese en-bloc clips I have.