What advantage would a 10mm necked down to .308 have over the 30 carbine?
.308-10mm auto would be more efficient in a shorter barrel. I seriously doubt that you'd be able to get 1800FPS from .30 carbine in a 6'' barrel, when the standard load is 1990FPS in an 18.5'' barrel. 9x25 Dillon, reaches 1800FPS with a 115 grain load in a 6'' bbl.
I just watched 4 videos of someone shooting .30 carbine from an automag with a 6'' bbl, and only one shot broke 1650FPS.
Also I don't see many auto pistols in .30 carbine. Seems easier to get a 10mm platform to convert to .308-10mm than finding a .30 carbine auto pistol.
Why? It's basically the twin of 5.7x28, which doesn't really impress me.
Bullets less than half the weight at the same velocity. Lighter for caliber, bullets of a smaller caliber. What's gained other than reduced recoil and possible magazine capacity increase, over the .308-10mm?