I have a 6mm Int in a Rem 40XB that carries a Rem 24X target scope; nice shooting rig. But, the twist is 14 in., I've never even tried to shoot anything heavier than 80 gr. and lighter with 4064 and Varget. The 6mm-250 isn't the same cartridge; the Int. has the shoulder set back about .1" from the .250 location.
The biggest problem you gonna have is forming cases for the (Walker) International. I made my own "forming die set" by modifying four other sizing dies because the form dies from RCBS were far too rich for my wallet.
Tell us your chamber is 6 Int or 6-250, and twist rate and I'll try to provide some data. But I can tell you now, 4350 is too slow if you have a 14 twist.
