[MaxMax]

I’d rather almost all the crud and most of the heat be kept
ahead of the piston in front of the gun.

There are some piston setups that don't heat up. I'll look into that another time
since that upgrade is way over my budget atm. Losing the rails for another grip
also concerns me for the AR.

[Spktyr]

Look at the Ruger SR556 - designed to have rails and a piston from the get go. It’s not a conversion.

Unless you’re right next to the gas block on mine, it doesn’t get any warmer than a DI gun’s rail.

Of course, I still regard the AR as a secondary weapon. My go-tos are a Saiga 12 and a DMR-configured FAL in .308.