Diamondback does not provide the weight of their 16" 7.62x39mm AR-15 Carbine Barrel. I would recommend contacting them directly for more information.
Yes. The Diamondback Barrels 7.62x39mm AR-15 Carbine Barrel is made from 4150 CMV steel which is a high carbon content steel, which makes it resilient to high-heat scenarios and with its abrasion resistance, the barrels wear slower over time.
The Diamondback Barrels 7.62x39mm AR-15 Carbine Barrel can shoot steel cased ammo but how well it performs would depend on the rest of the rifle set up.
Diamondback Barrels does not state if the Diamondback Barrels 7.62x39mm AR-15 Carbine Barrels are stressed relieved. They do state that throughout the manufacturing process the barrels are QC checked and then finished with a black nitride finish.