I have recovered 32 pounder shells and case-shot from a salt marsh at roughly 1400 yards inland from the beach, Ft Manhassett, Sabine Pass, Texas.
They were over 4+ feet deep, and at 2 feet we hit water. (In the process of cleaning and deactivating a shell, I dried out some of the powder-touching a cigar to it....boom.)
I have been told the flashpoint of black power is a little over 220 ° F, so when drying one out I am 50 ° {est} below that, because the thermostats for electric ovens are notoriously faulty.
Stephen Sylvia the publisher/editor of The North South Trader Magazine has been hunting, and recovering relics and projectiles for 40+ years. He deactivated and cleaned a 12 pounder Bormann
and went up to the kitchen, and turned on the oven to dry it out before coating it with polyurethane. A few minutes later the whole house shook; he went back up yo the kitchen to find his "wife's'" electric range
with the door blown off, and top, sides, and back bulged, but he had all the pieces to a detonated Bormann shell.
He's still married, wife got a new range.....and he is forbidden its use for shells. (I do not know if he can dry 'bolts' in it.)
Black Powder is the only powder classified as a "low explosive." You can lay a firecracker on concrete and hit it with a hammer and it goes off-that occurs because its so unstable that when compressed
it ignites. (Bags of nitro powder for battleship guns have a small packet of black powder on the ends to aid ignition. It is believed that when the number 2 turret of the Iowa blew up it was from the compression of those small bags--and to "ram" the large nitro bags in, the breeches......were open.)
Black power is easy to ignite and dangerous in most all circumstances. BE CAREFUL!
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HH