Real simple, the lock up depends on friction between the latch and shelf, add oil and instant poor lock up. THE number one fix for accuracy complaints reported by H&R gunsmiths at Gardner was "clean and dry catch", only we've been calling it a latch so long it' would be confusing to switch!! 
Tim
Agreed, just thing consistency, its key to so many shooting fundamentals.
Consistent lockup, consistant trigger pull, consistant for-end pressure, consistant screw torque, consistant cheek weld, consistant... Get the picture?

CW