What happened to the barrel? Was it over pressure or corrosion. Did it go bad in the loaded rounds?
Russ...
It was corrosion and it happened overnight. A barrel with less than a hundred rounds down the tube looked like it had been peened with a ballpeen hammer in the bore after running a patch through it to clean out the rust.
I had used 44N to develop a load the fall before. I cleaned the rifle meticulously as is my habit after every use. I also used the 44N in the 6.5x55 where it also worked well. The cases I was using back then were all corrosive primed so cleaning was a must as soon as possible.
The powder acted fine right up to the very end. Even on the day I shot it last. It was the next morning after the shoot that I cleaned it and noticed the bore condition. I talked with a couple of the others that had bought a large lot of this powder at the same time and one of them had similar results but in a cut down 303Brit. I went back to my records to check the other hand loads I had and started pulling bullets. Two other cartridge types had deteriorating powder in them.
That's when I went back to the powder I had in the magazine, which was a 24 cu ft chest freezer I had plugged into the wall of my shop. Temps were kept just above freezing during the whole time it was stored. It should have been fine. I had over 20 cans in there and all but two had rusty metal surfaces inside. I tossed all of it into my wife's flower gardens. Those blooms were super bright for several years.
There was another powder that was sold shortly after that gave issues as well. It was also a surplus military lot that was sold as 47N. It was the equivalent of N160 and a very consistent powder that worked well with heavy bullets in everything from the 308Win to the 338 Win Mag. It was a more modern Ball type powder that metered very easily. I really liked that powder and miss it still. Yes I've found a great replacement but that was an exceptional lot. It started to clump which isn't unusual but one day I noticed a very acrid smell coming out of the secure firearms room where I used to hand load. There was only one container on the metal shelf but the fumes escaping from it had caused the shelf to rust badly all around it. When I opened the container the powder had started to sweat and the smell was terrible. Very acrid. I check out the other two seven pound containers in the freezer and they had started doing the same thing, so they were relegated to the flower patch as well.
I have had similar things happen with commercial canister powders as well. All of them were containers I had purchased on sale from gun shops. Do I blame the shops??? No but I no longer purchase powder on sale without checking the dates of manufacture on the bottom of the cans.
The last surplus commercial powder I bought from Ammo Mart was listed as H414SL10. It is a great powder, suitable for a wide range of cartridges. So far it has stood up well for over a decade. It is extremely consistent as far as velocities go and I believe it was one of the fore runners of the powders which were later marketed as being temperature resistant concerning velocities. It is slightly slower burning than H414/W760 and is a Ball type powder.