I poured at least 12 lbs of IMR 4320 out on the garden a few months ago. Made me sick. I had bought up a bunch of it about 1990 or a bit earlier primarily for the 22 CHeetah Mk I wildcat. I 1st heard about the cartridge from an article written by Jim Carmichael form I think "Outdoor Life Magazine". Anyhow it used the special Remington manufactured small primer pocket 308 benchrest basic case and as such was prone to hangfires if you used just any powder and temperatures were low. Mr. Carmichael suggested combining IMR 4320 with Remington 7 1/2 benchrest primers for reliable ignition and it worked. So I went and bough 15,000 of the primers and two 8 lb cans of IMR 4320 to add to the individual 1lb cans i already had on my loading bench. They sat on my bench in the garage until about 6 or 7 years ago. This is a garage attached to the house that is insulated but not temperature controlled so the temperature varied a lot but not really that different than most guys loading bench that i know. Anyhow about 6 or 7 years ago I got concerned and did move all powders and primers to a temperature controlled storage except for 1 lb of each and 1,000 or less of each primer size that stays on the bench - in the garage - for use. Well, apparently something had already started happening to the IMR 4320 because even in a temp controlled storage area those two 8lb cans literally rotted and dumped powder all over the floor. Holes big enough to put a grape fruit through opened up in both sides of both cans. I was so sick about the idea of throwing it out that I kept using it for a while and developed a technique of separating the "Rust" - for lack of a better term - from the powder. I would pour out a small pile of the powder on a paper towel, then alternate lifting opposite corners of the towel letting the powder shift side to side. Each time it shifted part of the rust would sperate from the granules and I could pour the powder onto another paper towel. By repeating this a few times you ended up with what appeared to be good powder. And it loaded the same, gave good accuracy and no pressure signs. But then caution got the better of me and I dumped it all. I just don't know what characteristics may still be changing in the powder or how it would affect burn characteristics. What is odd is that I've yet to run into anybody else who has had this happen. Also I had 8lb cans of IMR 4350 and 4831 stored in the same place and for the same time that look like new. I sure wish they would bring IMR 4320 back though because it also works perfectly in the 35 Remington.
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Originally Posted by Burnt Fingers
