Now I'm quite willing to admit that I have never even seen a four bore in the flesh let alone ever having fired one, but...
With all due respect to the gent firing that cannon, I have to say that I have never seen anyone else mount a big gun the same way he does.
If you take a look you'll see he starts out with the barrels pointing at the sky, then pulls the gun to his shoulder with the barrels still way up in the air, then he lowers the gun down to take aim.
The ONLY other place where I've seen that type of gun mount used is with clay target shooters.
His stance is way too upright with too much weight on the back foot IMO.
I'm not disrespecting the guy at all, just making an observation.
He may well be a very good gunmaker but I just have to wonder how much big bore rifle shooting he has done previous to that video being taken.
One thing for sure is that there is no shortage of recoil with that gun!