Just an idea:

but the gun in an immovable vice. Make sure it's secure in the vice and that the vice cannot move when the gun is fired.

I mean it simply cannot move, neither the gun in the vice, nor the vice on whatever it's attached to. 100% solid.

Shoot it 3 times without moving it and that's (in theory) the precision of the gun.

I've always wanted to try this....is it a dumb idea?