Comparing bp recoil vs centerfire smokeless cartridge recoil is like comparing apples and oranges. They're entirely different things.
The bp felt recoil is lower in magnitude and lasts longer than the felt recoil from a smokeless cartridge. BP burns slower, so the felt recoil is not as sharp. It's more like a push than a punch.
You also have to factor in the details of the smokeless cartridge. My 3" S&W Model 60 .357 magnum has totally different characteristics when shooting a .38 sp 145 gr SWC practice round than when shooting a Speer Gold Dot 158 gr .357 magnum personal protection round.
I would classify 28 gr rb in an 1851 Navy as close to, but lower than, a .38 sp practice round. More than a .22 lr or even a .22 magnum, but less than the .38 sp Winchester white box round. But again, that's hard to do because the felt recoil is a different shape time history.