The only two Baker Hammerless guns I've recorded that are grade marked B are 186 and 444. I haven't recorded a gun marked A. Your gun looks to be a nice A to me. Interesting that your gun 408 has a 3-pin lock, while 1756, 1996 --

[Linked Image from i.imgur.com]

and 2048 have the "early" 1-pin locks.