I haven't bought BB's in 40 years, but they're probably not cheap either. Here's the other thing. Would you rather get hit by a BB traveling at like a 1,000 MPH, or a penny traveling at a 1,000 MPH. I'd rather get hit by a BB, so if I was building a bomb I'd use pennies. I was thinking broken glass bottles may be the way to go, but the explosion might turn the glass back into sand. I understand using the pressure cooker because that turns the whole pressure cooker into flying shrapnel, but how do you expalin to wife or mom where her pressure cooker is, and if you had to go out and buy one your right back to being cheaper using pennies.