Nothing wrong with an AR10 or HK-91. Wouldn’t waste billions of dollars and years of time getting the kinks out of a G3.
In the 80s I owned several HK rifles, I think two HK-91s. They were about as sweet shooting as a rifle gets.
I know they made a heavy barrel sniper version. The barrel was also longer, maybe 24 inches. Seems like that would be just about perfect.