Got one as well. Mine is a William Evans - who built yours?
Thanks to Ross Seyfried, his loads shoot four 740 gr bullets into sub three-inches at 100 yards (LxR/LxR). Tony Makris (Under Wild Skies) has taken several buffalo with his Paradox guns and Ross's loads. The H&H factory load does the same thing at 60 yards or so.
Haven't tried a duiker loading (No. 4 shot?), but it shoots lovely light mod patterns with 1 1/8 ounce no. 6 and smaller loads. As I have mentioned elsewhere here, at a waterhole in Namibia it rolled two warthog for leopard bait and created a mound of sand grouse in the last two hours before dusk. Incredible century + old technology.
By the way, you can order a brand new one from Holland & Holland for a base price of only 130,000 pounds sterling (that is 177,710 USD).
Did I mention I love my 110 year old Evans.