The .577 British revolver cartridge was the .44 magnum of it's day. It was the biggest, baddest, meanest pistol you could get, but wasn't to be handled lightly, and concealment was out of the question. All the big pistol makers made them, around Birmingham that included Webley & Scott and Tranter. The pistol loaded weighed about 8 pounds, with 5 or 6 rounds on tap. Pulling the trigger was like launching a Saturn V, you had to mean it.
There are a couple of these huge rounds up for auction. An early .577, with iron base, and coiled brass and cardboard case is on Auction Arms with a buy now price of $82.50. The revolvers for these early rounds had to have a steel plate inserted behind the cylinder because the primer would bulge out the back of the weak iron base and jam the cylinder. The drawback to the plate was that you had to dismount the cylinder and the plate to reload, then reassemble the gun. All this was solved when they advanced cartridge design to the drawn brass case. Now the primer would stay put and you could reload the revolver as normal. One of these drawn brass monsters is up for auction on Gunbroker, and is a bit pricey, as the buy now price is $140.00