Pulling left Why?

Rifle,CZ MTR 20inch factory stock ,acutac bipod,sand bags on rear,6x20x50 athlon
SK match red ,SK orange HV and Federal Gold standard
I’m having a issue pulling left this has become an issue with the MTR
I’ve tried focusing on what is causing this issue I’m leaning towards the stock just can’t get a good fit with it and I’m assuming I’m trying to adjust during trigger pull. Either pushing with my shoulder or pushing with trigger hand,any opinion or input would be appreciated very accurate when it comes together just can’t seem to get comfortable with the factory stock.
 
Rifle,CZ MTR 20inch factory stock ,acutac bipod,sand bags on rear,6x20x50 athlon
SK match red ,SK orange HV and Federal Gold standard
I’m having a issue pulling left this has become an issue with the MTR
I’ve tried focusing on what is causing this issue I’m leaning towards the stock just can’t get a good fit with it and I’m assuming I’m trying to adjust during trigger pull. Either pushing with my shoulder or pushing with trigger hand,any opinion or input would be appreciated very accurate when it comes together just can’t seem to get comfortable with the factory stock.
In what position?
 
Often caused by “shouldering” the rifle.
Sort of a flinch where you push it forward with shoulder as you fire.

In the past training indicated a firm grip with both hands and seating the rifle firmly in the shoulder pocket.
Today people seem to be less inclined to do that.