Gauntlet
They are certainly not projectiles fired from a revolver of the ABW period. Your additional info (converted to imperial grains - with which I am most familiar - shows that the weight spread is between 447 gr and 617 gr. That is a very large and heavy projectile indeed; the .45" MH rifle lead projectile ran to 480 grains (imp) and that for the MH Carbine a bit less.
What you describe as "steel inserts to the hollow bases" is, however, a clue. What follows is a bit dry, please bear with me.
Back in the early mid 1850's, when ML rifles (.702" P/51 and .577" P/53) were proposed to be issued across the British army, it was found that the soft lead, large calibre hollow based projectiles would not properly expand into the rifling upon firing as anticipated and were very inaccurate; little better than that of the smooth bore musket it replaced. The ready solution was to fit small, hemispherical cups into the hollow projectile bases; when the round was fired, the iron cup was impelled forward into the body of the projectile, expanding it into the rifling and improving accuracy considerably. My reading indicates that the iron cups were about .4" in diameter. Crude, but it worked. I am quoting here from the definitive book on the subject - "The English Cartridge" by Gibbons. A few years afterwards, 1860's, the iron cups were replaced by wood plugs - but that is neither here or there apart from a dating exercise.
It is possible that a similar idea of projectile-into-rifling base cup was used in other ML rifles - or perhaps even sporting rifles of old fashioned type. Outside my area.
To summarise what may well be an over-long reply, given the projectile weights provided (which fall into the 530 gr plus region of the P/51 and P/53) and the presence of the iron base cups, I think you have examples of projectiles from a much earlier era than the ABW.
Let me know what you think.
Regards
IL.
