You are a civilian, and you can do things however you want. Things are different in the military (get the supporting hand up on the barrel, or the RSM will give you a boot in the behind!
).Gripping the magazine promotes poor muzzle control. If you shoot that way, the forward hand essentially provides little more than a fulcrum and it's up to the right hand to pivot the muzzle around to engage targets. Put the supporting hand well up on the front furniture and it will serve as a natural pointer.
If you have much experience of trap shooting, you will see that most 'top guns' extend their supporting hand reasonably far forward, for the above reason. There are certainly exceptions, but typically they had poor initial training or a medical condition that prevented proper form, and they have learned to do well notwithstanding.
Long experience has shown that using the magazine of the L2A3 (aka Patchett, C1, etc.) as a 'handle' promotes stoppages.
