I have a 9,3x74R Merkel 150 (boxlock with side plates), it has fired 300-400 rounds. Three years ago the rifle doubled twice the same day with the right trigger. I sent the rifle to my gunsmith, and the trouble was a little burr in the left sear that prevented full engagement. A touch with the file/stone and no more problems up to this day.
The rifle arrived with a very heavy trigger pull (6-7 pounds in the right, more than 10 in the left), so my gunsmith lightened it to 3 and 4 pounds.
No more troubles, shoots fine, 2" or less at 100 yards with GPA ammunition.