25-06 to 264 win mag

I would prefer to convert the .25-06 to a 6.5-06 or a 6.5-06 AI (Ackley Improved). Same size .473.

The Ruger M77 MKII is a controlled feed bolt gun, & in .25-06 is of the length for .30-06 rounds

As mentioned the bolt face would need to be opened up and the extractor modified, an extra expense. The hardened steel bolt face requires some attention to open up.

The magazine box would need to be replaced with a magnum type. Comparing the .30-06 magazine boxes with 7 Rem Mag boxes it can be noticed that the mag box is fatter and the follower slightly wider. The stock would need minor modifications to accept the fatter mag box.

The 6.5-06 is a high performance round and is very popular meaning easy obtained brass using .25-06, .270, & .30-06 and relatively low cost dies. Lots of reload data available.

The AI (Ackley Improved) version gets about 100 fps more velocity but requires fire forming and additional expense dies.

Both rounds like H1000, RL26 with 140 grain bullets and RL23, H4831 with 120-123's and H4350, RL16 with 100's. More than adequate big game performance with 140's, fine long range yote/chuck with 120-123, and real good splat factor with 100's (3400 fps) but no prairie dog gun.

I would suggest, if more is needed than a 6.5-06 get a rifle chambered for a real big 6.5.
Easy way around that is the 6.5x280 ackley. Buy Nosler or hornady 280 ack imp and a pass through the die is all is needed. No fireforming.
Good practical solution.
I never disliked the 6.5-06 AI and would probably consider one now that more slow burning powders are available. On some of my ventures I pack 300 more rounds of ammo for up to 2 weeks shooting and like the ability to use common ordinary 06 brass. If I had a 6.5X.280AI I would use a F/L bushing die with a .288 bushing.