i would not be using the dried out powder ..... who knows how the burn has changed
I've had powder that was clumped and wet, but it was extremely acidic. Obviously bad.
I ruined a barrel on a lovely FWT M70 Winchester, chambered for the 257Rob with an old surplus powder from Higginson's, #44, which almost duplicates IMR3031.
I took it to a match loaded with the #44 powder, under 87grn bullets. No, the powder wasn't clumped when I loaded it, nor was there any sign of rust.
Two days after the match, when I finally got enough time to clean the bore, and the first wet patch came out loaded with rust.
After a couple of passes with a brush, the bore looked like someone had taken a ball peen hammer to it. The rifling was actually rounded off as well as pitted.
A friend of mine had some IMR4064 that got wet, when his basement flooded. It was purchased in an 8 pound jug and he liked to separate it all into other one pound containers. These containers were repurposed powder containers, with paper side walls and crimped on metal bottoms/tops. His basement flooded to the point that water was running out of the groundline windows, 6ft from the bottom.
It was the only powder he had on hand, as he only loaded for two rifles.
It had been soaking in the water for almost a week, before he could get to it.
The insurance paid for everything damaged, other than the powder.
He was loathe to throw it out. Just went against his nature.
He dried the powder on flat metal ''cooky trays'' in the sunlight, then put it all into a small pillow case and hung it outside, under cover for a week, giving it a couple of squeezes every time he walked by.
I was extremely leery about him using that powder but he had been using it in a 303Brit M95 Winchester Lever for years and was confident in it's ability to handle at least one high pressure round.
The first round he loaded was exactly the same as he had used for decades, with 180 grain bullets.
Nothing had changed. POI was as close as could be expected with open irons at 100yds, so he went home and loaded up 20 more, with the same charge/bullet/primer and several times fired cases.
It took him close to five years to use up that lot of IMR4064 and he never once said anything about deterioration or change of POI.