some times people put 20 ga shells in the vests and for get them. when they use it again,and have a 12 ga,they unwittingly load the 20 ga,then the 12ga shells,and they pump it.when they go to shoot it slides farther down the barrell.it doesnt hit the shell they think it dry fired and there isnt a shell in the chamber. now,when your trying to hit a buck, your not going to go"wait didnt i pump it?",theyre going to be thinking"please dont run away,please dont run away, please dont run away..."as theyre pumping the 12 ga shell.boom!make sure you have the corect ammunition for your.firearm before loading, shooting, or even carryingshotshells or cartridges