For example a semi-automatic machine gun, versus a target rifle

target rifle:
http://www.2158atc.co.uk/assets/images/l81.jpg

Guns used in recent shooting:
http://imgace.com/wp-content/uploads/2012/12/guns-used-by-adam-lanza-in-shooting-owned-by-nancy-lanza.jpg
Edit: Both can kill, that is undeniable. However, some are designed to rapidly kill as many people as there primary purpose, for example a machine gun (i.e. light, small can be carried easily, many shots per minute), others are designed for extreme precision (long, cumbersome, heavy, don't have adequate sights for sniping but could kill in this fashion).