Uh, there's
plenty of taper in the
7.72x39 case. This has much to do with it's reliable function in AKs, a positive shared with .303 Br and .30-40 Krag once AKA ".30 Gov't", AND like the design's intentionally loose tolerances to accommodate ease of manufacture and indifference to sandy or muddy conditions. (
the genius of the whole AK concept!! thus ..
the original 'World Gun' )
IMO it's coolly ironic that CMMG's 'Mutant' and Savage, Ruger, CZ, and Winchester have chambered rifles in "7.62x39", but in reality might be bored/chambered for .308"
OR the interchangeable .311-312" ammo/bullets ... heck, even die sets are offered with FL sizers for .308" AND .311" bullets/chambers with this in mind. :thumbsup:. (Was it Win & Ruger that were .308' bore? .. others)
Whatever was discussed earlier about 'brass vs steel' says that like any other ammo it can be had cheap, and/but
your gun(s) may or may not like 'X' or 'Y' like any other firearm and ammo combo!! There are those few among who will reload steel
HG cases once, maybe twice, evenBlazer aluminum cases
once, but that almost always just to prove it can be done.
If you like 7.62's ballistic envelope, why wouldn't you be shooting the easy-peasy .300 BO
ballistic twin with 125-154g bullets already??
IMO, 7.62 is the one 'clinker' cal for AR-
15's, while 10 others make .223 look like coyote, prairie pup, fox, and bobcat medicine, but what might be 'missing' is
more AR-15-pattern options in .22 Mag.

(Ruger AR __s seem to be 'jeweled' gear.)