[John Sabato]

Remove the right grip and test fire the gun to the last round. Does it hold open? If so, the right grip will require that some wood be shaved slightly to allow free movement of the magazine follower button at the top of its travel. This button is what pushes up the holdopen to lock back the toggle on the last shot. If your symptoms remain the same, especially with 3 different magazines, I would suspect that either the ammunition is underpowered (not very likely) or that the mainspring may be just a tad too powerful or too long preventing full travel of the toggle when fired.

Also inspect the hold open notch on the underside of the breech block, and the hold open itself to see if the edges are damaged or overly worn so that it will only catch when the toggle is gently pulled back by hand.

Let us know what you find...