RobD: Mosin-Nagants don't have collars, do they? Haven't pulled one apart for a few weeks but quick look at parts diagrams don't seem to show either front or rear collars. As to other actions, the P14/ M1917's, of course, have collars and, as ChuckinDenver points out repeateadly in that forum adjustment of the lengths of both front and rear collars are crucial for accuracy with those rifles.
Ridolpho