Daryl,
Correct indeed…….the Lewis is a “brass case” rifle hence the larger bore/groove diameter.
Paper case rifles were on the order of ~.835” whilst brass case rifles were of a larger actual bore maybe ~.845”-.855” (~.875”in the groove) due to the thinner case mouth and resulting slightly larger ball/bullet diameter to fit said brass case.
The rifles were typically referred as to “bore” based upon the usual overall shotshell dimensions -vs- actual true bore diameter. The original buyer was expected to know whether his rifle was a brass case or paper case version.
Given the use of a round ball I’d imagine either type ammo would function safely (maybe not accurately?) in either type bore or chamber.
- Mike