Mercury reducers affecting accuracy

[Win42]

I have a RUM 300 Remington BDL with a wood stock with a Barnes mounts and rings with a Nikon Monarch 4x16 x 50. When I first got it, it kicked like a mule, always coming back to touch me on my head. So we put a Kick-Ez recoil pad and a mercury reducer in the stock. The recoil has reduced tremendously. But before we put the mercury stick in, it always grouped 5 shots within an 1.5 to 2 inches of each other at 100 yds. Since we put the stick in, it shoots all over the board, the first shot would shoot two right, then another further right, then the next one back left four inches. Would putting a mercury stick within the stock be the cause for this?