And looks as if the muzzle-boring was off centre, deeper on the bottom 1/2 of the bore, than on the top 1/2. I thought at first this lack of visual rifling might have been due to the focus not showing the lack of rifling on the bottom 1/2 of the muzzle, but the bottom 1/2 does appear to be in focus and there are no grooves showing.
The rifling from 1/2 way up, to the top, appears close to 1/3 of the grooves missing.
Please advise if this is the case, or not. We can only go by what we see.