Have you checked the detents if they are worn ?
My 2.1 is completely stock, stock settings, and is very smooth. Never had problems in low temps, but then i was using winter paint.
You cannot slow down the bolt action on the 2.1
@ what velocity was the 2.1 shooting (FPS) ?
You could lower the FPS a fraction down by 10 fps. This would help slightly when playing in low temps.