<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: natesfitness</div><div class="ubbcode-body">If the bullets are the same caliber am I able to use any 308 barrel to rebarrel my rem 700 300 win mag or am I missing somthing? </div></div>
If you have a .308win chambered barrel you could ream it to .300win mag. Of course, if the .308win is a mountain rifle contoured barrel, or similar contour, there isn't enough barrel stock to make that work.
Also need to throat the barrel once you've reamed it, and probably finish the chambering by hand to get headspace you want.
If you have a heavy contour barrel like a Palma, might consider just parting off the .308win chambered area if it leaves you enough for your win mag chamber.
That said, probably not worth paying someone to do all that work unless you have a like-new barrel. Many barrelmakers and Brownells will sell a short-chambered barrel which needs only the last few thousandths of chamber reamed in order to set headspace, or supply them with your boltnose and boltface to receiver shoulder measurements and get a Rem 700 threaded, pre-fit barrel that is brand new.
You also need to make sure the barrel has a twist rate tight enough to make the .300 perform to it's limits, and enough barrel length to achieve velocity levels that will give decent performance with the .300.
Basically, a 20" 1:12" twist .308 barrel would be pretty pointless if you reamed it to .300 Win Mag, but a 24" 1:10" .308 barrel would do good with a rechamber to .300.
I'd shy away from anything shorter than 24" or any twist looser than 1:10" for a .300.