Remington and DuPont set up the ADI Mulwala explosives and Footscray ammunition plants during WW2 to assist Australia in manufacturing ammunition used in the South West Pacific operations theatre and thereby reduce shipping requirements of heavy loaded cartridges from the USA. Naturally, Mulwala made powders were in effect identical to those manufactured under the IMR name and used for the same purposes. Over the intervening years, the products have diverged due to R&D work, and both companies have changed ownership, IMR also moving north of the US / Canada border.
IMR and ADI / H versions of the same product number, eg 4350, 4831, 4895 do roughly the same jobs, but aren't the same things. Some are shown as having identical rates on burning speed charts, some vary slightly. The 4831s have the greatest difference inh this respect due to a historical accident. The early Hodgdon operation started with surplus US manufactured propellants, mostly DuPont IMR extruded grades, but the occasional Winchester Western ball type (Ball Lot-C manufactured for a British contract for .303 Mk7z ball, later more or less replicated as BL-C(2) for Hodgdon). When the surplus products ran out, Hodgdon had to find alternative manufacturers, and DuPont was opposed to supplying the handloading market at the time. Hodgdon went intially to ICI Nobel in Scotland and when that plant was closed, to the now privatised ADI. In each case, the remit was to make similar grades, so today's 4350 is two removes from that of the 1950s and might vary considerably. The 'accident' with the 4831s was that this was the last of the first generation of surplus numbers to run out and over the considerabler number of years that Hodgdon stored it, it gradually changed its moisture content and became slower burning. When Hodgdon then went to ICI Nobel, it asked for a slower burner than the still in US production fresh IMR version as handloaders would be confused and very likely run excessively high pressures by using pet loads worked up on the surplus stuff.
ADI / Thales has put a great deal of R&D into its Mulwala powders and the greatest advance for many handloaders as weell as military users is the temperature countering work. That's mainly why the H versions have become more popular, plus a lot of good marketing work by Hodgdon powder before it took on the same job for IMR (General Dynamics owned these days). ADI responded earlier to customer requests for shorter grain sizes to allow more consistent metering in both home and factory reloading. Also, VarGet hit an almost unique niche that guarantees excellent sales and excellent brand loyalty to the H. brand - IMR has had no direct equivalent. IMR now appears to be upping the ante - it likely has to as it's not recreational requirements that drive expensive R&D programmes here, more often military - and soldiers want complete temperature stability as well as very consistent charge weights in their ammo these days, so everybody's trying to catch up with Hodgdon, including IMR.
As all IMR grades are single-based types, they're mot particularly temperature affected anyway, but the new Enduron grades should cancel or at the least reduce the gap with ADI.
IMR-4895 is not faster burning than H4895 in most cartridges (Relative burning rate is variable according to application, not fixed.) In most mid sized cartridges, it allows the use of slightly higher charges and achieves higher MVs. It's also very flexible with a huge range of uses, and as such partuially compensates for ADI / H. having two useful grades in this bracket, 4895 and VarGet.
WD
