I shoot a Trubor and had this problem when I first got it (couple of years ago) They would all fire the second time through, I had loaded around 100K rounds on my 650 before that so I was kinda mystified. Then I changed my loading procedure, when seating the primers, I do a "double tap" on the handle (pushing it forward twice). I have not had a light strike since then. The press was clean so I imagine that I was either getting lazy (or old, or both) and occasionally not pushing the handle all the way. Try doing this for a while and if your light strikes go away, good deal. If not, punt.