Are you planning on trying the powerbelts in your great plains rifle?
If so please let us know how it turns out. I'm building a GPR right now, and even though its main use will be paper punching where a patch an ball would be fine, I'd like to know what it would do with sabots, or maxis.
Don't know what a finished rifle costs, but there was an add in the kit for my gpr for exchangeable barrels. You can switch calibers and twist rates, fast or slow for about $180 ( I think, don't have the add with me right now) They may not be browned yet though.