Originally Posted by Pnumatix
As I read it. You changed out the stock, rifle shot well the first outing, second time not so good. Then you had the stock bedded and rechecked the mounts (torqued etc). First time out it shot well, second time not so well.
Still sounds like the Talley's might be the source of your troubles. Retorque them again and see if the same issue presents.
As I posted above I have had this issue myself. I also went the B&C Medalist route. I even went back to the one inch Tikka supplied rings for a while and the problem went away. Tried an EGW rail. It stayed put for longer but the same issue cropped up after about ten shots. The amount of movement I was getting was tiny. I could only just feel it and it usually only became fully evedent when removing the rings for another mounting exercise. The groups just opened up with no real change in zero. I think the flat surface on the Tikka receiver which has grooves running the length of it that reduce contact area between the bases even further, make for a poor mounting arrangement. They are fine with dovetailed mounts, but struggle with any that rely on screws alone. I eventually sourced a rail from the Tikka Perforamce Centre that had a steel stud that located in the blind hole machined at the forward end of the receiver. It was an interference fit and had to be tapped in gently with a hammer. It has never given problems since (300 plus rounds).
By the way I torque all my Tikka B&C stocked rifles to 55"lbs, bedded or not.
Thanks for the reply. Pretty much here are my 4 trips to the range so far after the B&C stock was installed
1. Rifle shot well about 3/4" average between 4 different groups
2. Groups opened up to about 1 1/2"-2"
3. Had rifle bedded since the second trip and the groups shrank to around 1/2"
4. Groups opened back up to around 1 1/2 to 2" again.
At no point in time have i removed the scope or rings. I would agree that the mounts could be a problem if the rifle didnt shoot so well during trip #3.