Note: By 'speaker', I mean the piece of hardware from which sound emanates, NOT the Muslim himself. Not advocating violence here!
I'm quite sure the call to prayer will be played from a tape recording. Crosman 760? Yikes, that brings back memories. Amazingly, they're still cranking 'em out. Too small a caliber, though. Check online for some of the customized CO2-powered Crosmans - pellets as large as 9mm are available. Then there's the "potato cannon", which could be modified to launch pickled pigs' feet...