I found this on the USA Shooting web site
Shooting bum (shoot' in bum) n.[ME shoten < akin to ON skj-ota,Ger schiessen Ger
bummler, loafer, habitually tardy person<bummeln, to go slowly, waste time] 1 one who engages in the activity of sport shooting to the exclusion of most other conventional lifestyles 2 often sacrifices career,money,or spouse for the freedom and travel associated with life in the fast lane of the shooting world 3 commonly found on the road or at bars, shooting ranges or other unpretentious hangouts; heavy concentrationsoccur in certain clubs, universities and marksmanship units
4 often found with the nicest people in the world--other shooters!!