Not positive this fits, but there were numbers of dif methods employed trying for tighter patterns before choke boring became standard. I have read of sabboted or wrapped shot charges being used in the 1870's~1880's I think. There may be a ref to that in Michael Yardley's book 'Clay Pigeon Shooting: A History'. Michael or Dig may have some better knowledge on the subject. Of course, Eley is still in business too and they may have a historian. Anyway, I'd think that is what you were looking at rather than something made for muzzle loaders in any generic sense, tho it certainly could have been. Without knowing the 'as built' diameters of the two charges, it could have been intended for muzzle loader, breech loader w/brass cartridge or breech with paper, tho from gauge markings would say the latter unlikely, so that leaves muzzle loader or brass cartridge as most probable.
And .. as Russ was prone to saying, "But I could be wrong."
