A full length strain screw and original spring will bang CCI primers every time. First check is to make sure the screw is turned all the way in. If it is loos turn it all the way tight, and that should cure the issue. As most already fire, as little as a quarter of a turn could make the difference. Non the less, turn it all the way tight. It that does not fix the misfires, check to see if the screw has been shortened. If it looks like it has been filed, replace it. That should fix your problem.

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Richard Gillespie
FBINA 102