Originally H4227 was a large lot of bulk IMR4227. Manufacturers use the bulk lots and load to specific velocity and pressure levels and adjust the charges to meet that goal. Handloaders don't have pressure testing equipment to do the same so powder companies blend various "lots" of the same powder to give a consistent can to can result so you and I can load basically by the specified "charge" despite how many cans of powder we go through. When Hogdons original supply ran out, they had it duplicated overseas. Though I can't be sure, the earliest duplication was I believe in Scotland and of late, most likely in Australia. Traditionally, H4227 is a tiny bit slower than IMR. In my use, Hogdons seems be little more consistant in delivering accuracy and can pretty much be substituted for any charge listed for IMR. Using IMR for Hogdon requires a charge reduction then working back up.
