Gunsmithing 7mm rum to 300 mag

[Ragin_cajun]

I have a 7mm rum and I don't want it. I want a good ole 300 mag. Now my question is, how easy is the change going to be?
I need a new barrel anyway so that's not an issue. From what I have researched the bolt face is the same. Am I correct? Is it a basic barrel and having the new chamber cut? With a new barrel the gunsmith will cut the chamber and take care of head spacing so it seems like everything can be done with a barrel swap. Am I off or will it really be that easy?

 

[Rifletuner]

Everything you have described is correct. Boltface will work, get a barrel blank and have the chamber done.

However, assuming its a repeater you also need to look at the magazine. The larger RUM case will mean the 300 (I assume you mean Win Mag?) is narrower in the body than the RUM, so 300 rounds will most likely not feed correctly if the magazine is untouched.