No. These usually just float.

From the photos, proof marks, and number, this is a quite early .450 NE from Osborne, almost certainly pre-1900.

This is Osborne SN 51112:

http://www.champlinarms.com/Default.aspx...&GunID=1679

This Lawn & Alder is Osborne SN 50208, and has post 1904 London proof:

http://www.gunsinternational.com/Lawn-&-Alder-Boxlock-Double-Rifle-450400.cfm?gun_id=100072794

In my research records I see an Army & Navy .500 NE ordered from Osborne, Osborne SN 51289, sold 12/17/06.