I'm not quite clear from your post what was upsetting about the guy's actions . . .
Did he shoulder you aside? Cut in front of you in line? Take a carton out of your shopping cart? What?
From your post it just sounds like ammo was available in larger cartons or shipping boxes, and with no WalMart help around, the guy was proactive, opened the large carton, and took several boxes of ammo, presumbably to be paid for at the counter up front . . . whereas you were waiting around to be served.
From personal experience at WalMart, the wait for service can be QUITE long, so unless there's something not included in your post, I'm not seeing a problem here.
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