John,

The rifles are quite similar, but there are subtle differences. Both are back action, hammer, Jones UL double rifles, the climax design of the black powder double rifles. So in that sense they are much the same.

Let me catalog some differences.

Chamber:
Watson .577 3" BPE
Henry .577 2-3/4" BPE

This gives the Watson a slight edge on ballistics. Standard ballistics of the day, comparing solid bullets, provided for the 3" round to fire a 610 grain bullet at 1650 fps. The 2-3/4" round fired a 560 grain bullet at 1650 fps. So there is a bit more payload with the longer round.

Weight:
Watson 12 lbs. 3 oz.
Henry 10 lbs. 2 oz.

The Henry is quite noticeably lighter and handier. The Watson is wider across the breech and more massive. For carrying all day, choose the Henry. To soak up recoil, choose the Watson.

Barrels:
Watson 26" fluid steel, Enfield rifled
Henry 28" fine Damascus, Henry rifled

Other dimensions and attributes:
The Henry has a length of pull 14-1/4"; The Watson 14-1/2". I'm tall with long arms, so the longer rifle fits me a little better.

The Henry's butt is checkered and fit with steel heel and toe plates. The Watson has a horn buttplate.

As for styling, the Henry is distinctly a Henry rifle. It has the exaggerated pistol grip so typical of Henry, and it also has steel heel and toe plates of a classic Henry double. The Watson is styled like a London gun. If it had flat sided hammers it would be indistinguishable from a Holland & Holland of the same period. Other London makers used round sided hammers and made essentially the same gun. Earlier H&H rifles are found with round sided hammers. The Henry is a best quality build for a maharajah. The Watson has somewhat less embellishment.

The Henry was completed October 11, 1890. The Watson was completed in 1896.

Both rifles have London BP proofs. The Henry was made in Edinburgh. The Watson was likely made in Birmingham, but it's impossible to know. Watson may have had made it themselves in London.

The Henry is housed in its original case with a full compliment of loading tools. The Watson is without a case.

So you see, they are much the same, with noted differences.

Curl