CLAY SHOOTING LESSONS
What you are doing is see-sawing with the muzzles. This problem is one of the most common mistakes shooters make when mounting the gun.
As they bring the gun up into the shoulder, they drop the muzzles down under the flight line of the target, and then rush to bring it back up and chase the target.
While mounting, the muzzles should not drop at all but remain just slightly under the flight line of the clay/bird but moving onto the bird at the same time.
No matter which technique your using those muzzles must stay on line at all times.
If you learn to mount into the cheek before the gun enters the shoulder as it should be done, this will help to eliminate the problem.
Also stop lifting the gun with the back-hand only while balancing it on the front hand.
Use both hands to lift the gun parallel.