I'm curious, how much ammunition is being used in this trade or business?  I would guess the number of shots fired for business purposes would be somewhere around 0.

The answer may depend on whether you're on the south side of Chicago (I hear it's the baddest part of town) or nearby Naperville, IL (listed by Forbes as the safest city in the US (with 100K+ population)).  It may also depend on what's being "couriered."  Drugs?  That's a hard "no" under IRC 280E.  IRC 162 simply refers to "ordinary and necessary expenses."  Are these ordinary and necessary?