In 1975, Dupont stopped the production of powders so all Dupont marked cans were manufactured prior to 1975 in 1/2 lb cans.
IMR (Improved Military Rifle) took the line over so the 1/2 lb cans began the marking of IMR, 1976-2003.
In 2003 Hodgdon acquired IMR and then started the 1 lb plastic canisters.