Same thing happened to my friend. He had ahammer extention. TC says it can cause this. But what caught my eye is he had no problem with federals even with the hammer but also had trouble with winchester CT's. The win primers are a little tougher than most however. Theres a few websites that deal with the problem that sells heavy trigger mechanisms and talkes about the issue. Its not all that uncommon with the encore.

http://www.bellmtcs.com/store/index.php