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IMR 4350 powder

Not a stupid question at all.

IMR (Improved Military Rifle) smokeless powder intended for reloading of sporting rifle ammunition. Military ammunition is also loaded with IMR powders, but generally the surplus military powders do NOT correspond directly with those available from IMR canister powders. The number is one originally assigned by the manufacturer (DuPont) to the powder with a specific burning rate/chamber pressure/ under bomb calorimeter test conditions.

They are single-base nitrocelluose smokeless propellents distinguished by granule size, perforation size, and deterrent coating.

I believe the IMR series is identified by burning rate, with the lower numbers (IMR 3031, 4064, 4895, 4350, 4831, etc) designating fastest to slowest burning rate under a specified set of conditions.

Adjacent number IMR powders can actually switch places under different load conditions in the same cartridge caliber.
That is, burning rates are not absolutes, but are variables.

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