Galli, I think Mike Bailey is spot on both on sale value and insurance value for you rifle..

I have a similar double in .475 from the same time span (another make), a little more upmarked with scroll engraving all over the action and mint barrels. It is insured for GBP 10.000,-

Barrel condition is the most critical parameter for setting a value. As Cal Pappas say (he is a capacity on old doubles..), the only item that cant be fixed on a double is worn/rusty barrels..

Due to the present decline in African hunting, due to low oil price and lots of bad press against hunting, workin man double rifles do not sell so easily...

Top end doubles sell like hotcakes....but they are put away for investment..