As I recall, but could be wrong, the A grade used a wedge bolt, same as the Nitro rather than the rotary of the NID. As most of the rotaries weren't really properly fit up they served only to keep the bbls closed, so they offered virtually no advantage over the wedge. On the other hand the rotaries are about the only ones I have ever heard of becoming "Self-Openers".
As I understand it other than some fit & finish, main difference between the NS & WA was the NS used a forged steel frame while the WA's was made of mallable iron. Though this is not as desirable as forged steel, they do seem to have held up well & given good service for the money.
