liverwort,
The 5.5mm Berdan primer is .217" and large rifle Boxer primers are .210. Immediately after the war, Berdan primed cases were converted to Boxer primed by swaging (with hammer, punch, and a rod inside the case to act as an anvil) to displace enough metal from the Berdan case anvil and sides of the primer pocket to close it down to .210" and a flash hole was then drilled. Most cases are now available Boxer primed.
Mike