here is how to search the US patent office records for firearms related patents when you know the date, go to


http://patft.uspto.gov/netahtml/PTO/search-adv.htm


so for example if you want to search for a gun patent (classification 42) and you know the date
August 12, 1876


type in

isd/8/12/1876 and ccl/42/$



and click on the box that indicates you want the patents before 1976,


and this will give you all the firearms related patents on that particular day.