No theory, just some facts about a rifle I had...
In the early 70s I got a Mauser 98 in .308 Win.
Built by our local gunsmith Red Johnson, on a military Mauser action. Red put on a .308 Win barrel with Williams sights, a fairly rakish Fajen stock with a rollover cheekpiece and an agressively hooked pistol grip. Drilled and tapped and put on Weaver Tip-off mounts and a 3-9x scope.
Sold it to me for $140, generously allowing me $90 credit for the Winchester 190 I traded in. Him being friends with my dad, and a distant cousin might have had something to do with that, but that though never occurred to me until many years later.
No work other work was done to the action, nothing done to the rails, or the magazine, in fact, I hand to put the slope on the military follower so it wouldn't lock open empty.
I added a Numrich scope safety and a Jaeger trigger (couldn't get the Timney I wanted..)
That rifle functioned FLAWLESSLY. Fed EVERYTHING from 100gr plinkers to 220gr RNs. There was no block in the mag box, and, by today's standards it had a long throat. There was no "chasing the lands" on that gun. I could seat 180 RN to the full length of the mag box and they never hit the lands. What they did was allow for more powder in the .308 case and yes, I was running above listed book values.
Never an MOA rifle (in those days, damn little was) but a good solid 1.5-2MOA with any decent handload or factory ammo. Took deer just fine and a surprising number of woodchucks (with the 110jhp and 125 spitzer) at ranges 300 and under.
Main points, on THAT rifle, no alteration to the mag box, follower or extractor needed for feeding, it fed .308 flawlessly.
Another rifle might need more work, that one didn't and because of that I wouldn't automatically assume you HAD to do work on a .30-06 to get the .308 to run well in it, other than change the barrel.
