I would be interested to know what type of rifling was employed in these weapons?

The earliest descriptive references I can find to rifling was that by the Frenchman Delvigne in 1826. This is 50 odd years after the American War of Independence!

The British did not adopt the Brunswick rifle until 1836, which was a complete failure for military purposes, even though it was successfully used by Purdey 20 years later for sporting rifles.

Spurred on by the abject failure of unrifled muskets in the Kaffir Wars in South Africa 1n 1846 where it was estimated that it took 3,200 rounds to disable a Kaffir, the British finally adopted the Minie rifling system in 1851.

One wonders why they it took 75 years or so after encountering these Pennsylvania rifles, for them, and the rest of the world to devise workable rifling?

BTW - as I noted in my post, the Indian Mutiny was in 1857, and the Jacob Double barreled rifle was developed during the 1840's. It was not given to Indian Army "Sowars" ("Native" Troops), because after the Mutiny, the British did not trust them enough to give them weapons that were superior to what was issued to the British Army.

As to why the concept was not apparently taken up by other Armies, there can only be conjecture.

If I may indulge in some; the cost must have been very high - the example I have seen was made to a very high standard. I understand they were made by George Daw, an English maker of very high grade sporting guns.

The fact that they were not finally issued for military use, does not neccesarily say anything about their suitablity for that purpose, but what cannot be denied is that they were DESIGNED for military use.

Their popularity when sold off for sporting use, may just have been the genesis of the sporting double rifle as we know it today, derived as it is from British origins?