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Correct - I think BP has been classified as an explosive all along, but I've been told that reg's changed after 9-11 and that's why most places stopped carrying it.

You are correct - BP substitutes are considered flammables, but not explosives - just like smokeless powder. BP was reclassified shortly after 9-11 which is why so many gun shops now don't bother carrying real BP - they would be required to have special storage facilities, etc.