Chango -- It was explained to me as what happens on a sxs when you don't release the trigger far enough between shots that the second fires, almost like doubling. Anyway both barrels fire and it kicks like hell.
The original use of an inertia block was to prevent this. A clean and undamaged sear and hammer notch are also important. I suspect that the Gun Dr. could look at the hammers and sear and fix the problem quickly.
If it were my gun, I would try two or three different things and see if they worked. If they didn't, I would then send it to Gun Dr. He could fix the original problem and the other things I messed up trying to fix the first problem.
I did mention to Bill that at times, some shooters (a very few) do have problems with the faster mechanical triggers, like the Krieghoffs and Kolars. Those shooters tend to be trigger "squeezers" and not puller/slappers.
A trigger squeezer never gets enough pressure on the trigger to keep it in the rearward position long enough through the recoil movement.
Edit--I just read the original post to the Coach. I see the gun was previously work on. Could be a trigger problem right there--DB