Ah!

'Rough chamber' theory possibly busted.

Slide action guns have a little feature called an 'inertia lock'.

The idea is to prevent the action from opening until a shell is fired, or the shooter operates some sort of 'action release' which can be either a latch lever, or simply moving the slide forward as it naturally wants to do under recoil.

After the fifth station, did you change technique at all? If the inertia lock is causing the problem, try a heavier load on the first shot.



"The price of good shotgunnery is constant practice" - Fred Kimble