Just to add my R0.02 worth. The common wisdom is to first really TIGHTEN the screw in front of the mag before inserting any of the others - this is the one that takes 90%+ of the recoil so it needs to be snug. Thereafter any others - but these do not need to be as tight as the first.
We have also found a number of 602s and 550s with one or both pillars missing causing all sorts of accuracy and functional problems. We carry spares which any gunsmith/machinist can make.