It's the smell of .45ACP cartridges being disassembled at the rate of 600 per minute. To wit:

That is me shooting the Thompson M1928 at the Big Sandy Machine Gun shoot. It would be a bargain at twice the price of $20 per magazine. I could have spent all day there. Did pretty well, too; I hit many a barrel and even single shots were pretty easy once I got the hang of it.

And note the finger that came out of the trigger guard when I thought the mag was empty. That's some style there, if I do say so myself. Remember, kids: If you aren't shooting it, don't be fingering it.