BFJ,
Is it really possible to have that sort of weight distribution on a double?
Come to think of it, I do remember a double which had been built from a shotgun and the rifle barrels were sleeved full length inside the shottie tubes.
It was a 444 Marlin chambering and I reckon that double may have had close to equal weight in the forward, center and rear thirds.
My .470 is a European double and it's proportions and style are similar to many English doubles.

The Hambrusch sure shoots nice.