Shoot me a message if you're looking to get rid of a .20 practical (preferred) or a .204 I'm mostly looking for a lighter weight rifle or upper to use as a walking predator calling rifle.
The 20 Practical doesn't give up much case capacity to the 204R. Here is a picture of a 204R with a 40 grain V-Max bullet seated to factory overall length and a 20 Practical with the same bullet seated at the same overall length(AR-15 magazine length). The bullet in the 204R has to be seated well below the neck shoulder junction, about .130" giving up valuable powder capacity compared to the 20 Practical. Looking at the picture, I don't think there is really too much difference case capacity between the two of them when loaded to function in an AR-15 magazine.