Hi JPK

Thanks for Your data.
Your double isn't the first handy one grabbed from the shelf, Marcel Thys is a very renowned maker. Even more a rarity in the USA than in Europe or Belgium.

Don't be ashame about Your 458 caliber. My PH in the CAR was using a Heym in 458 also, a Lott but a 458. Now he is using my Weath 460??????? Sure I don't regret it. Everybody has to bear his own cross

I don't doubt that the 458 has plenty of ooomph and is far sufficient for elephants. It's the rimless version of the 470, not less not more.
Now it's time that I calculate again. Your barrel are 66.6 cm long, a current measurement is 67, what's fairly long for a double.