.... I can't really comment on the sniper use of the swivel, but certainly, and this if from my own observation, in the early 50s the Australianicon Military type target shooter did. From the prone position, the web sling was shortened and looped around the upper forearm of the off hand ( Forming a triangular support system). Much the same effect, presumably as the US 1907? style sling "loop" . ( Then the Lithgow no.3 SMLE rifles dominated, with just the odd No.4, with the Canadianicon Longbranch being the believed best, due to stronger, superior steel ) ..... David K. ...