Tip: don't wrap your thumb over the top of the pistol grip. Place it gently on your first finger.
When
slowly pulling your trigger finger gently backwards, make sure you're not inputting any 'squeeze' with any part of either hand.
Squeeze is the group killer, it is taught by the military to enable soldiers to get the trigger to work on a standard issue rifle. You DO NOT want to squeeze.
Have a look at the many examples on YouTube who disengage the thumb, they are reducing any input into the rifle.
The next area to work on is 'where is your mind' when pulling the trigger.
Nothing complicated, was the shot a surprise when the shot broke?
If it was not a surprise, then as the cross hairs moved over the target, you moved your mind onto pulling the trigger and thus were able to monitor and predict the trigger break.
Focus on the centre of target area, ( your mind will keep pulling the crosshairs back to the target centre) start the
slow pulling of the trigger, DO NOT monitor the trigger pull. If this produces an unexpected shot release, excellent! You have moved on in your marksmanship development.
Control of the weapon can be maintained by one or more of the following:
Shoulder against the butt (pushing into a bipod).
Employing a sling, I use this one, probably the best in the world.
https://ultimategunsling.com/
Pushing onto a 'fifth leg' of a quad stick system.
When shooting targets on the bench I use the first two, when hunting I use the latter two.
For hunters who shoot in cover that reaches the waist, I think the guys in the US should look at the quad stick development that has taken place in Europe in the last ten years. It can produce stability that can almost equal benchrest shooting.