There was some debate in this forum a few years back as to whether IMR and H4198 had become the same thing as some IMR bottles were labeled as 'Made in Australia', not Canada.
AFAIK, the cause / story wasn't resolved, but if there was a switch or merger, it appeared to be short-term. Most IMR powders are still allegedly made to the original Dupont recipes, but are now made in Valleyfield, Quebec Province, Canada by General Dynamics, Energetics Division, Canada. If they retain the original form, they are unusual in that every grade produces the exact same amount of energy per unit of weight, and they vary only by burning rate which is controlled by kernel dimensions, diameter of the central hole in each kernel, and deterrent coatings weight / thickness.
IMR-8208 XBR is a Thales / ADI manufactured 'Extreme' powder grade from Australia and logically should therefore be in the Hodgdon range alongside H4895 which is close to it in burning rate terms. However, it was put into the IMR line-up and called '8208' because it was allegedly a new-manufacture equivalent to an old lot of surplus Dupont IMR-8208, manufactured for some special purpose 5.56X45mm loads that the BR shooters dug up from somewhere and which was the 'must use' powder in the 6PPC for a while. In the event, Hodgdon might as well not have bothered because the production lots of 8208 never replicated the original IMR version and the BR guys didn't adopt it. Trail Boss is another Australian export but for marketing reasons has been called IMR.
GD Valleyfield either responding to Hodgdon requests or more likely at their own initiative with Hodgdon agreement, is developing a new range of 'Enduron' powders which I suspect might in the medium to long run replace 'legacy' IMR grades. IMR-4451 is the nearest 'Enduron' equivalent to IMR-4350 for instance. They incorporate a number of desirable features for today's shooting world such as being less affected by temperature than traditional IMR powders and have an anti-coppering additive. However, what may be the real behind the scenes driver is that they have gone 'green' and the traditional chemical additives used in older powders (Hodgdon and IMR) that start with Di ... have been replaced. These older chemicals are toxic / carcinogenic and environmental regulations are slowly banning them from one country after another. All of Europe will do so in the not too distant future so all Australian manufactured Hodgdon rifle powders, most St. Marks manufactured Hodgdon / Winchester ball powders, and all 'legacy' IMR powders will be barred from all European Union countries both as handloading components and within factory ammunition. Eventually, the US will fall into line too one imagines - few governments like to be seen to be 'anti-green' these days - so General Dynamics is getting its new 'clean' grades up and running now. All European manufactured propellants have already been 'cleaned up'.
