Thanks fellas. I suppose that could be happening. The difference is negligeble, thousandths or less but enough to prevent detonation of the primer in the loaded cartridges. Didn't make it to the range today so still don't know. Hoping the nose job on the hammer takes care of it though.

I was using both reloadeds and factory loaded ammo with the same results from both. The expanded neck could be hanging it up just enough to make the difference though and closing the action seating the (empty) cartidge just enough to close but still shallow enough to catch the striker. In fact this is probably the best explaination as the loaded rounds drop in with that thunk, thunk that is so reasuring when loading a double. The empties however do not. I had assumed it was merely the extra weight of the loaded rounds... maybe not eh?
The chambers are reamed with a minimum dimension reamer. The supplier actually cautioned that some ammo with sloppy tolerances may not fit properly... You just may be on to something! I've been so hung up on headspacing on the rim I hadn't thought of the expanded necks. Thanks!