The British 303 cartridge of all ages are head spaced on the rim – really a rim space, which is inter-changed with the bolt head for one with a different (target) length – As an older design. the rifle action is “failed cartridge safe” by design – the rim space limits are also very generous by design and manufacture (with war time relaxations) to allow all grades of ammunition to chamber under all conditions. Tightening and "over head spacing" (rim spacing) is probable and th