There is evidence that reloadable solid brass pinfire shotgun shells,fitted with an adapter designed to take a standard percussion cap were at one time available.... This type of shell would be easier to reload than a standard paper pinfire case which requires special tools to remove the spent cap and press home the replacement.
The Charles Parker "T-Latch" was the first commercially made American breech-loader circa 1866-68, which began (s/n 06 at the Meridan CT Historical Society)) as an externally primed caplock using a 2-inch 12B-size brass shell with a tiny Maynard-type pinhole in the base of the shell. Very soon (circa early-1867) the next generation of Parker-specific shotshells would have a musket nipple built in to the base to receive a common musket cap. These centerfire musket-nipple shells were referred to in the early literature as "coned."
The coned shotshells preceded the Berdan and Boxer patents for primers, and were multi-piece, soldered together, and relatively expensive. Paper pinfire cartridges were relatively cheap. I doubt that the pictured pinfire/musket-cap adaption was to save money or reduce the reloading risk, but was likely to allow the shooter to use commonly available powder and musket caps where special pinfire ammo components were not available.
I had in my collection (until sold last year) examples of the Maynard-type pinhole cartridges, and the "coned" one-off Parker seminal centerfire cartridges (one with the cap still on the musket nipple). And I also had a pair of latter-day (circa 1890s) musket-nipple steel shells that some British Lord of the Manor might have taken to Africa on Safari, as a hedge to running out of his paper Berdan- or Boxer-primed shells or the special primers.
Musket caps were always available everywhere, at the far corners of the earth, and I suspect that the seemingly unique musket-cap pinfire shell pictured was to hedge the possible shortfall of special pinfire ammo far from home.
There are pictures of all the seminal shotgun ammo scattered throughout Parker Guns: Shooting Flying and the American Experience
...all except a "coned" pinfire shotshell, which is certainly European, as is the Lefaucheux-style gun. In this context, the coned pinfire shell did not precede the common Lefaucheux's-patent pinfire shell, but was a latter-day adaption for reasons stated. EDM