IME 264 win mags are notoriously finicky as with most seriously overbore calibers. I've had 2, sold one and rebarreled the other to a different caliber. The factory ammo is anemic at best and has a LOT
of head clearance for a very sloppy fit in the chamber
Remington quality is not what it used to be but can be MADE
to shoot with a lot of effort. Of course, some will get lucky and have a shooter right out of the box but most consider the Remington useful because of the design of the action/bolt and fast lock time. Most Remington factory rifles I have dealt with have been long throated, short shouldered and large case bodied chambers. All of which can be dealt with.
You can have the action squared at a gunsmith relatively cheap and that is not something you should do yourself. Then you can buy a box of Acraglas and bed the recoil lug, the action just behind the recoil lug at the action screw and under the chamber portion of the barrel. It is skeery the first time but with lots of release agent it is not that hard to do. Torque the screws down to the recommended foot pounds. Then free float the barrel with judicious use of a dremel.
Once you do any of this or reload for it the factory will be happy to tell you that it voids the warranty but I doubt you will get and good results from them anyway.
That and reloading will more than likely make a huge improvement. The dies that I like to use for making straight ammo are not available in 264 win mag (Lee Collet/Redding Body Die) but you can have them made fairly cheaply or go the conventional route with expander balls and standard dies.
A pre-64 Winchester Model 70 in 264 win mag was the reason I started reloading many years ago but don't own one now.