Leaning back in the Golden Armchair and lining up the six-pack of Kokanees just in case I need additional creative license, I'll have a whack...

As long as case neck relief is adequate {might require neck reaming} the case support should be greater. Problem is, the internal volume is less. So from what I've read, improvements are not as great as they might appear to be at first blush.

As an aside, I am not certain that all heat treatment and steel alloys are the same between the .307 guns and the .30-30's.

Maybe a better over-all plan would be to; use .375 cases as you suggest, then reaming chamber to Ackely-improved specs. Then, careful load workup. This might be a very cheap option for a fellow who wants to boost performance.

Of course, that boost is probably NOT going to take the round into .308 Win territory, but might get the round closer to .300 Savage territory.

Also, one intriguing aspect of your thought comes to me in the form of using tricked bullets, i.e. HEAVIER bullets with tricked tips.

Last I checked, the Marlins used a 1/10" twist in all their .30-30's. I think a really neat option would be to get some Hornady 220 grain bullets, add a cannelure if necessary and cut them back to produce a DEAD FLAT point. This would give a "short" bullet that would function thru the magazine {proper OAL} of about 200 grain weight, easily stabilized in the 1/10" and due to the tricking, give superb expansion and deep penetration even at the say, 1850-1900 fps that might be possible {maybe...???...2000 fps? with modern powders?}.

Sort of a "Magnum .303 Savage".

I really like your idea.

Cheap, interesting, a very useable, not to mention, a properly done Ackely-improved job will leave you able to shoot regular .30-30's.