Hi

In service during WW11 the head space was allowed to creep over 74 thou to a max of 80. This does increase the recoil, but basically the case on firing shouldn't move back in the chamber by more that 20 thou and the service spec was set as the rim thickness on service ammo can vary.If you get a an unfired case and use some imperial feeler guages and a dab of Araldite or similar you can make your own up.

Hope this helps

H