Re: 300wm to 338 edge
I am not a gunsmith, but, I would recommend having a smith mill out the back of the receiver in the magwell 0.110 in order to install a Wyatt magbox for the longer COAL. Also will need to shorten the bolt stop the same 0.110.
The boltface will work fine, there is only 0.002 difference in base diameter of the cartridges. Kevin Wyatt has instructions included if you purchase the magbox from him. Just do a search for Wyatt Mag Box.