The military chamber for the 7X57 suck's for most of us in the US. I would have my own reamer made to specs for the bullet you want to shoot in a good brand of barrel. The 6.5X57 would be my choice as I love the 6.5 bullets. I first built my 6.5-06 in the mid-80's, since the 6.5X57 needs a medium or long action I had a M70 that I rebarreled to 6.5-06 as I had a good amount of 06' brass. I was lucky to find a Douglas barrel that had been sitting a long time in a gun shop in that "odd" bore size and got a very good price, I won a medal at the NRA State High Power Match with that rifle in my class.