rechambering

[saskshooter]

what caliburs could be built easily on a .300 win mag action?
I have a remington and a winchester actions haven't decided wich
one i'll use

[Rapier]

Without modification, the 300 WM action can be chambered for any cartridge with a standard Mag rim diameter as long as the OAL of the cartridge will fit in the magazine with .020 to .050 free space (bullet nose to magazine front wall).

Without modification, the standard Remington 700 allows for a longer cartridge than does the standard 70 Winchester, due to the center screw configuration used in the Mdl 70 triggergurad.

A lot may depend on what bullet weight you want to throw. If you want the bullet seated no lower than the neck base and intend to use a heavy bullet, you may need all the magazine length you can get.
Ed