I've heard (and read) they are the same too. I've never loaded any H4227 (it was gone before I ever got to try it), but a lot of IMR 4227. I have used some H4227 data to load cartridges with IMR 4227. I don't load 'really' hot so wasn't a concern. For example, I really like Taffin's load of 20g of 4227 under 250-255g bullet in .45 Colt. He states H-4227. I used IMR-4227. YMMV. Safe in my guns.