There are a few companies making 7.62X39 barrels
As far as the dreaded bolt breakage there are good 7.62 bolts and not so good. The MGI bolt is generally considered GTG. Having said that I have been running a inferior DPMS for over 2000K and seems to be chugging along. I Magnufluxed ( dye penetrant ) it recently and it looks fine .
If you doubt you can open a AR style bolt to a 7.62X39 and have a reliable bolt you need to talk to Bill Alexander from Alexander Arms...6.5 Grendel, 50 Beowulf etc....( he is very eager to share his knowledge ). The reason you don't see 6.5Grendel bolts failing all the time is all the 6.5Grendel bolts that come with ( Saber, JP Rifle, Satern etc ) all the Grendel barrels are from his him. That is part of the licencing agreement. You can't buy a 6.5Grendel without using his bolts
Bottome line is its ok to have a large bolt face, you just need to use a good bolt !
This is the same for the 458 socom that is open all the way to a 308 case boltface
As far as magazines, the whole discussion of the 30rd CP mags not fitting in mag pouches is laughable since we pin them to 5 anyways. 5 mags will feed fine out of standard AR mags BTW.
You can also use the readily available 6.5 Grendel mags. Mine run flawless with 7.62X39
As far as corrosive ammo goes, I can see why you don't want to do all the scrubbing in the bolt and carrier group ( I hate cleaning guns ). Don't care about the gas tube since they are $15. I use a chrome carrier now so it wipes out easy. The inside of the reciever is give it a quick scrub with a toothbrush and it seem to be working fine
I would say this is the only downside of a 7.62 X 39
The other downside would be since ammo is cheap, you tend to blow way more off so you really don't save money in the long run !