If you are talking about Muzzle Jump when using a sandbag or rest, it can be caused by placing the rifle with the rest under the front of the forearm. The nature of a break action is that they tend to flex a bit when fired. This causes a springing effect that lifts the muzzle. Shoot your rifle with the rest under either the hinge point, or as far back under the forearm as you can, instead of the front of the forearm. If your rifle does not have a good lockup, it magnifies the tendency. Good Luck.