Quick question, isn't H-4198 an extreme powder? If so then the extremes didn't come around until 1992-93.
If talking old forgotten powders IMR-3031 and IMR 4198 have been around since before WWII. IIRC
H4198 wasn't always an Extreme powder; it's been around quite awhile along with the IMR version. They're actually quite a bit different in some cartridges now (like the 45-70 for instance.)
According to what I have been able to find so far is that H-4198 didn't show up until hodgdon manual #21 which was printed in 1970-1973, will confirm when I get my copy of #20 printed in 1967. Also found that most powders made that early were from Nobel in Scotland that used a different deterent coating which was when the IMR powders of the same # were different enough to warrant the warning not to use IMR data.
Fact is Hodgdon never made any powder, he just bought Mil surplus and pull down powder from 06 rounds(4895) BL-C from 303 British, and a slower powder from 20 mm cannon rounds (H-450, or maybe H-4350).
So if you bought powder from hodgdon prior to 70-73 it's a good chance you were just shooting repackaged IMR or Hurcules powders that were made for the military.
