You can get any of them in a carbine !Come on folks! This isnt a question on caliber. Either one would work fine, its a question of the gun. Brush guns need to be short, light would be nice but not exactly necessary.
Actually that would be the .307 Winchester. It is literally a rimmed .308 Win (made to fit in a lever gun).It is pretty much 7.62x51R. Yes, that is correct, 7.62x51R
The problem with the .307 Win is that the rifles it was chambered in were short of action. The .308 Marlin was developed specifically to get similar performance with a better bullet from a normal .30-30 sized action. There is a pretty significant difference between the FTX bullets meant for the .30-30 and the .308MX. The .307Win can use the .30-30 version, but not the .308MX version, and still function through the magazine. Not a huge deal for a true brush gun, but for someone wanting a more flexible rifle with longer legs, it's something to consider. That said, my .308MX Marlin is a basket case. I couldn't recommend one at this point..307 Winchester. Find one of those.
Really the .307 Winchester, the .307 is basically a rimmed version of the .308 Winchester cartridge with thicker case walls. The .30-30 all together different, but they three of them can use the same bullet.....Because as you said. The .307 can use the 30-30 version and not the .308 MX version. Being that the .307 is equal to a .308 I think it would open to soon.
I said in another post that we have loaded Speer 170 grain FN meant for 30-30s using IMR4064 in .30-06 for a poor mans Ballistic Tip, and also for youths in the family we'd load them down to around 2450 fps. Nevertheless I think there are better bullets than the FTX design. i.e. Not a fan of Hornady bullets in .30 caliber.