You might try ArmaLite. When they first started up with the AR-10 they advertised no sale of ArmaLite AR-10 lower receivers separately, only the complete rifle but they had a lower for sale mfg. by "Eagle Arms" and they did sell the rest of the AR-10 parts.
You might contact them and maybe they will give you comparative specs.
You might contact them and maybe they will give you comparative specs.