Can't really count the modern repro blackpowder irons, so I won't mention them...
Oldest "modern" irons ('smokeless powder')
1954 Romanian M-44 Mosin-Nagant
1955 US Rifle Cal .30 M1
OLD Marlin 99 .22LR...no S/N
1962 or so Vintage Mossberg 500
Don't own it, but have shot a budd's lever-action .32-20 Been so long since I shot it (1973) I don't remember if it was a Marlin or Winchester, but that action was smoother than hot butter