Re: can a winchester model 70 action in 30-06 be changed to a 300 wm?
If the action is a Mauser style (Pre 64) it would be easier, With a Push feed model 70 it's harder.
Both boltfaces have to be opened up to accept the larger diameter case. The Push feed would have to have a Sako style extractor installed. The Claw extractor on the post 64 would also have to be trimmed back to fit the cas as well.
Then the bottom of the action would have to be opened up so the cartridges would be able to feed out of the magazine and the feed ramps reworked as well. I beleive a magazine block would also have to be installed to properly stack the cartridges in the mag.
There are some problems with using a long action for a short fat case usually in the feeding from a magazine. I have a friend who built a 6.5x300WSM on a Rem700 long action (so he could seat out the bullets) and he could never get it to feed correctly, he ended up getting a Winchester Short action and pulled the 300 WSM bbl and rebarreled it to another 6.5-300WSM.
So, It could be done, but with lots of work and extra $$$ and there is the chance of problems with feeding.
Hope this helps,