Cesure - I hadn't thought of the Ruger rifles specifically, but you're right. Modifying one of those might make it a lot easier. The only problem would be if you wanted more than the few rounds offered by a rotary mag. In a low recoiling round like the .327 (from a rifle) you could run the action without moving the rifle from the shoulder. Not quite as fast as a semi though it should be fast enough.
BillCA in CA (Unfortunately)