Master Lock makes a series of warded locks that are often used outdoors, because they’ll function when left in a forest to get rained on and nested in. You’ll probably find warded keys like this one on a park ranger’s keyring:

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Take that key, grind the bumps off everywhere but the tip, and it’ll open every lock with that keyway.

As for tubular locks, the pick looks like this:

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It’s not difficult to use, you jam it in the lock and jick it around until the lock opens. What’s happening is you’re setting sliding elements on the tool to the pin heights in the lock. Once the lock opens, the business end of the tool now closely resembles the key. The tool can be read to make/buy a proper key for that lock, or you can tighten the collar to lock it down and now the tool functions as a key.

Or you buy the right key, which is what OP did. It’s not like the cases in Wal-Mart are all keyed different; the corporation probably orders keys and locks in lots of tens of thousands so I bet there is one tubular key that’ll get you into most if not all Wal-Mart cabinets; maybe the guns and ammunition are stored behind a different key, MAYBE. Actually glance into that kind of thing and you’ll find out just how useless locks are. There’s a key known as the CH751. Almost every RV or camper’s exterior baggage doors are locked with a CH751. So are arcade cabinets, gumball machines, voting booths…just about anywhere someone is going to put a bullshit little mass produced lock cylinder it’ll probably be a CH751, if they don’t replace it with an equally bullshit tubular lock.