Daryl,

my gunsmith shoots and services mostly the small calibers that the locals here use on roebuck. His biggest gun is a 6.5 mm, from what I remember. As a result, he is was overly afraid of the .470 and actually showed up with a lead-shot padded vest (which is not even necessary with my gun as it has a very effective recoil pad). So, being inexperienced with big calibers, he mounted the gun low into the padding of his vest because he thought he needed to. Of course it had the effect that you described. As I was standing behind him while he shooting I didn't catch it early enough to correct him. He apparently also flinched violently as he ended up hitting the ceiling as well. Unfortunately for him, we were also testing loads that are a bit on the stiff side for a .470 (500 grain GSC FN solids at almost 2300 f/s).