Well, the fact that revolvers have all the cosmetic moving parts (cylinder that swings out, hammer) results in gas system designs that are significantly more complicated and less beefy than GBBs. And yes, GBBs have greater gas capacity as well.
I certainly understand the desire to field something different. You just have to ask yourself if it's worth giving up a good chunk of functionality in return.
"The Bird of Hermes is My Name, Eating My Wings to Make Me Tame."