So, has this one been done? A quick google didn't turn up anything. I've got a Marling 336 that I have not yet got to shoot to my satisfaction and a barrel change may be in order. I don't care to sink much into this project and 30 cal barrel are a lot less expensive than 35's. Love the 35rem but if I have trouble keeping them on a pie plate at 100yds, something needs to change. FWIW this is a 1956 vintage RC model that seems to have a loose spot in the bore.

Not looking for any hot performance, just would like to keep a decent rifle going. I'm going to give fire-lapping a try but just thinking of options if that doesn't work.

Sounds like you want to rechamber a .30-30 Win barrel to a necked down .35 Rem case, right? The .35 case necked to .30 will be about .115 to .120 thou short of useing up the neck of the .30-30.Still might shoot OK though. If you want a .30-30 24 inch barrel Gun Parts Corp. had them pretty cheep a while back, might still have them. If you want to start with a freash barrel blank, plan on a few hours machine time. Might be better off to just peddle it and look for a 336A in .35 Rem. Damned nice rifles.

I would just go 307 Win just a little more case capacity. Your 35 should shoot better than what you are getting, I would touch up the crown.

According to a Brownells catalog the Douglas 35 cal. barrels are not that much more than a 30 cal barrel..If an old Marlin won't shoot I think your always better off selling it and buying what you want..Projects get out of control financially, trust me on this.

Rechamber to 356 Winchester, perhaps?

The 35 Remington necked down to .30 will give about the same results as rechambering to 300 Savage. The savage is a bit larger in diameter but a tad shorter. If you want to improve the ballistics over the 35 but drop to a .30 caliber You would be better off going to the 308 or in a lever action the 307.

Go big!
400 Savage!
410-300 Savage