The rifle has to fit you. I am fortunate in having "standard" body dimensions so that most rifles and shotguns right off the shelf mount and swing easily for me. Same can be said for golf clubs. I can get them off the rack.
I have 2 doubles. The favorite is a .450/400 Jeffery's. I can shoot it much like a shotgun meaning that I practiced snapping it up to shoulder and banging off two shots as quick as I can without taking the time to fine aim with the sights. Call it shotgun style. Practice in case of a charge at short range. As long as I mount the rifle and get a good check weld, I can hit a 4 x 6" index card at 25y with both shots every time. Is it NOT my expertise, but rather the fit of the gun. I have a SxS 28g scatter gun that I'm pretty handy with. I have a Spanish made O/U AYA that I got at the factory and the craftsmen there fitted me personally. I can't hit jack with it. Got another O/U I shoot fine.
There are 2 great attributes of a double. First is the instant availability of a second follow up shot. The second, and let's be honest, is the romance and mystique that goes with them. Maybe we should add the man sized big bore cartridges that they swallow are an attraction. Also, a double with 24" bbls is shorter and handier in the thick stuff than is bolt gun, especially with a scope. So it does have some advantages.
Is it essential for DG and Africa? No. Doubles were the choice for thick skinned DG back when the Brits ruled East Africa. The advent of the .458 Winchester changed the game to the point that by the mid 1960s the double gun industry was more or less dead. A rifle in .458 could be had for 1/20th the cost of a British double of any grade.
I am also a big fan of British made doubles. Those from the Continent do not seem to fit and point as comfortably. The Brits do it better. Better than Heym, Merkel, Ferlach Guild, Sabatti, Chapuis or any other I've handled. My Jeffery's was built in 1909 and shows that at one point in its life it was used regularly and often. I wish it could talk. The bores show abuse from the mercury primers in the old cordite loads that Kynoch made, but the gun is tight and regulates as well as it did the day it came from the factory.
Scope on a Big Bore double (sigh). I will personally horse whip any of my buddies that try stunt. That would be like Marilyn Monroe with a strap on. Somebody might be into that, but not me! Beats the purpose of having Marilyn Monroe. (Kate Upton if you can't bring back a 25 year old MM from the great beyond).
I have killed Cape Buffalo, and their cousins the NW Red Buff and Forest buff with a wide range of cartridges. I've brained one with an 8 mm wildcat. Killed one with a 9.3 JDJ (once was enough, though it was effective). I have taken down a couple of buff on the run after they received a shot with a bigger bore with a .338 WM. Both high shoulder shots that collapsed them instantly. I have had very good results with the 9.3 x 62. However, when I went on a multi buffalo safari in Tanzania, I took the Jeffery's. Walking in tall grass, tracking along thick riverine bush all made me appreciate the double's instant available second shot as peace of mind. Same for Forest buff in Cameroon.
I'm a sucker for the romance of the double rifle for DG, but anything from 9.3 x 62 to .375 to .416 are good. Hit them where it counts and the rest is easy.
