Grendel barrrels for a bolt action......

[tackdriver]

I would suggest Jim at Apache Gun works. I am not sure if he does Mauser barrels but it would be worth looking into. I know he uses Green Mountain blanks a lot. I got a .260 rem barrel from him a couple months back and it is the most accurate gun i own now. He has very competitive prices(I probably saved $175+ over a Shilen) and his turn around time was 4wks+/-