Came across some extra info, hte rules an regualtiosn for these sports in 1933.
We stillc ompete at SLR much the same as it was then, however the rings have shrunk and we only have baloons on the fences to represent an enemy,not a whole dummy.
http://s827.photobucket.com/albums/zz199/DPuckey/1933%20Mounted%20Skill%20at%20Arms/The Pathe links here show both SLR and Dummy Thursting in action.