Best to make a simple cast with some parifin wax first. Plug the bore about an inch or two in the barrel above the chamber. Melt some parrafin wax and pour in intil it is even with the chamber. Allow to cool an hour or so and push it out with a patch or wad on a cleaning rod from the muzzle. You can use a micrometer and measure it out and compare to some of the publications or online reloading sites and confirm. 6.5x52R has been a popular caliber in Europe though it has roots with the winchester 1894. Great little deer cartridge.