I had no idea it was that simple to "convert" a 7MM Rem Mag or 300 WM to .264 WM. I feel stupid for not knowing that.
So there's literally nothing else to it? Buy one of those guns, remove the old barrel and have a 6.5MM barrel installed, and voila, you can shoot .264 WM?
yup. exactly. Cut-rifled barrels like Brux, Bartlein , etc are preferrable to button rifled. Send them your old barrel and they can duplicate its profile if you are keeping the stock. If this is a BDL you'll probably want to keep it looking stock cuz they are nice looking.
If this is your hunting rifle, pick the length that gives you the balance you like. You give up a little speed (<100 fps) in a 26 vs 24 inch, but gain comfort. One is not more accurate than the other.
What is most important is the twist. A 1 in 8 twist is necessary to stabilize the nice high BC bullets like Hornady's 143 gr ELD-X or Nosler's 142 ABLR (my choice). You can stabilize higher weights, also.
Practically nobody makes decent factory ammo, so if you don't reload, find a vendor like Colorado Custom Cartridge, Buy a couple of boxes of factory ammo, go target practice, sight your scope, get a feel. .... then send them the fireformed brass to be reloaded. If your smith has put your custom barrel on a trued action, you will have a serious shooter, sub-MOA, that reaches out to your target with high lethal effectiveness... and not much recoil. It is a wonderful caliber, capable of taking anything you want in the States Enjoy the ride and save the old barrel for posterity.