Savage. Get yourself a Savage bolt gun in a “long” action - .270, .30-06, etc.
Why Savage? Because you can change the barrels and headspace them yourself, without a ‘smith, and that matters if things get kinky.
.270 or .30-06 because the long action calibers have brass available in abundance (the .270, .280, .25-06, .35 Whelen, .338-06, etc) are all based off -06 brass.
All these loads have more than enough oomph to do anything you need in the lower 48.
Savage rifles give you the most accuracy for the money. Purists don’t like them because of the barrel lock nut forward of the receiver - it looks ugly to fans of the Rem700 and Win70 rifles. Yes, it’s ugly.
But you wanted a SHTF rifle, and one has to think about parts and repairs.
Got a reference to a writeup on how to do that?