the fact that the 10x60R 400 will be the cartridge that makes the most sense do not mean it must be right but I see no other possiblity now. there is a 10x52R and a 10x56R but this were target rounds made from 11,15 Mauser brass - 13 mm base diameter, 15 mm rim, 2,5mm rim thickness.
horneber does not list the 10x60R! he would make it but you have at least two years to wait.
if you cut try to load an original cartridge you would know for sure it works. find a collector round now for 50 euro here.
use the time and send the chamber cast to Dave at CH4D. let make you an offer for die set. Dave have seen a lot of thingsand he would give you good advise.
I would use 9,3x74r brass, reduce the base diameter on the late( its thick enough), cut it to 60 mmm
maybe rim thickness is a little bit to much, try it
I think that there are 10 mmm neck reamer on the market, the formed case have to be reamed out.
will come in when having more time this evening
Last edited by pwm; 06/22/11 11:11 PM.