Bullets are the parts of the gun that cause damage. If they are not in the gun, they cannot shoot out of the gun and tear through a lampshade or some pancakes or your buddy’s butt or a kid.
“Checking” is when you make extra sure you really did the thing you thought you did. Did you do the thing? If you did, you can say “Check!” Or not. You don’t have to say that.
Locks are a way to separate guns from The Wrong Hands. The Wrong Hands could belong to a kid or a criminal or a jittery cowboy or a cute monkey in a sailor hat. There are a lot of Wrong Hands out there. Like, tons.