When I first fit this action onto the frame I had slack side to side... I Kept using feeler gauges until I found one that it would not lock up on... I went to the next thinnest gauge and made my shim from this.... After gluing it in place with JB my action would close and not lock up... I checked the latch engagement by using chalk from a carpenters chalk box... I saw there was no lines on the latch... I worked it with a file until my latch would snap into place... I went a little deep on one corner of the latch shelf, but it locks up tight and solid on a .0015 feeler gauge now....