Originally Posted by F106 Fan
This kind of failure to fire can also be caused by not having the primer fully seated in the pocket. The firing pin just moves the primer further forward.
It seems hard to fathom but apparently it is possible.
I agree with Richard, it was probably a high primer if it fired the 2nd time fine. If Win or most other primers are seated flush or below they ussually go off with stock gun and springs with no problems.