Please no "you should not have bought a Hatsan" comments, not on this post.
The Gun is a good 4 years old, is of the old design and is a semi auto in 12 gauge. Designed as a Sec 1, not converted. (That is a knew stock not the original for this shotgun).
Over this weekend the gun has started slam firing. It is firing a second shot as soon as the bolt is back home, but so far only the one second shot - it has not gone full auto.
On one occasion it fired a second shot when I released the trigger from the fully pulled back position to normal position. This only happened the once.
It is not happening every time and not always on the first shot.
The gun has been apart and looked at by a group of very experienced Sec 1 semi auto shooters, but unfortunately they are not familiar with this gun.
There is no damage to the firing pin or the firing pin spring - nothing sticking out to contact the primer.
The trigger mechanism appears to be all correct but I can not help thinking that this may be where the problem is.
Any thoughts?
As a side topic, the loading gate on this model was always a bad design requiring a button to be de pressed for every shell loaded. The new Gate / trigger mech is a better design and dose not require this to be done, working more like a Remi 1100. Should anyone know if the knew assembly can be put in an old gun I would be interested.
I know both Chuck and myself contacted Hatsan when they first changed but I got no feed back and I don't think Chuck did either.

DM
PS - We were lucky to have few shooters on the range today and I was able to shoot without anyone else on the point. I was supervised at all times and safety was the name of the game. Once all obvious avenues were explored we called it a day.