little date problem here. The NRA was founded in 1871 by Northern Republicans to lobby Congress to pass the 14th and 15th Amendments. I might add by Northern Republicans to counter the Southern Democrats and their KKK. It might also amuse you the MLK and Malcom X were registered Republicans.
All I know from history is that the NRA was founded because of the abysmal shooting of Union troops during the War of Secession. I don’t know the actual date of founding but it was of course after the war.