I only have one, .223/556 RRA, and am in the process of building a second in the same caliber, pre-election. The intent is to move the RRA back to a closer-range configuration, and the build will be a precision long range one. Currently the RRA is bastardized for both tasks as it is my only one.
If I were to introduce a second caliber, it would be a 458 SOCOM.