Doug
I know what you mean by "chugging" on full auto weapons.

Back in the day, a buddy got a RPB M10 carbine chambered in 45 ACP. It was a basically a M10 with a fixed metal stock and long heat shrouded barrel.It even had a flash hider cone.
It was so much fun to shoot.It just chugged away on full auto. Very accurate and not so hard on the ammo budget.
The standard M10 and especially the M11 (380 ACP) zipped thru a magazine in a few seconds!

I have never seen another of those variants,gotta be rare. My buddy swapped it for a Sterling long ago.

Fun days!
Bob