I certainly haven't seen them all, but I'll venture to say that perhaps no more than about 10-15% of the vintage .450/400's of either ilk were made on the so-called smaller or scaled action made specifically for the .450/400 and other cartridges with the same case-head diameter. I've only seen two, one in .450/400 (3,25") (bearing the Army & Navy name but on a long-bar Webley action) and one in the 3" version. The latter was a stunner: Watson Bros on a small-frame screw-grip action, deep-relief Kell-engraved, spectacular wood, 24" barrels, ejectors, and all together a lovely package. From a distance, it looked more like a .303 than a .450/400. A friend shot a buffalo bull with it in the Zambezi Valley before selling it to another collector.
The problem, for lack of a better term, with the .450/400's is that many were so-called trade rifles, made for export to the colonies and not necessarily bespoke rifles for individual customers. Most of these were made on larger, .470-capable actions, and they were overweight. Many of the Jeffery's that I've seen, especially the Thomas Turner-made ones, followed this recipe. They certainly don't recoil very much, though.
Many others were made on smaller actions, and they are generally very fine rifles. Like Dewald mentioned, 10 pounds or thereabouts, good handling, and nice to shoot. A friend of mine here in Australia even owns a matched pair of .450/400's. Made for Lyon & Lyon on smaller screw-grip actions, they are, as he is fond of saying, the ultimate gentleman's accessory.
