Originally Posted by russc
Sear spring is usually the fix when I have this issue. QEVs can also exacerbate the problem. QEVs are not good for mech cockers, IMO.
What is happening is your backblock is moving forward quicker than your sear can raise up to catch the hammer.
I've learned this frustrating lesson well over the past 2 days when I installed a roller sear and new slide frame on my mech cocker with ram/qevs installed.
Removing the qevs made all the difference in ease of timing.