There is a lot of difference in your 10 gauge load and the load used in 1874. The powder used was black powder, although 4 to 5 1/2 drams is a stiff charge no matter how you look at it.
But, when I said light load I was referring to the 1 ounce of shot to 1 1/4 ounces. which is very light in a 10 gauge. And I was comparing it to a 1 ounce 28 gauge load used today.
Pete