5.6 X 52R (in Europe). Slug your barrel to be sure, but I think it is going to take a .227" diameter bullet. I do not think anyone has a jacketed bullet for it so it will be a cast bullet item only if it is .227". They are based on a 25-35 case
The only data I have is for a custom Mauser that takes .224" bullets. A 55 grain bullet and IMR 4895 is a starting load of 31.4 for 3300 fps or so. It says you can go up to 34.6 for 3600 fps, but that is more than likely pushing it pretty hard.
I also have a load of 13.9 of IMR 4227 for 2100 fps with a FMJ 55 grain. You will get around the same, maybe a little more with a hard cast bullet with a gas check.
http://www.montanabulletworks.com/224_Rifle.htmlis one source of cast bullets that are 60 grains and .228" diameter. I am guessing a little based on the 55 grain data (old Hornady #3 manual) I have. I would think that 14.0 grains or there abouts of IMR 4227 would be a good load for the 60 grain cast bullet with a gas check.
Good Luck and Good Shooting