Its an imaginary passphrase into the world of the knowledgeable about firearms. Context: Ha! Stupid NEWB doesn't know the difference between a clip and a magazine. Oddly, you seldom see it when it come to"bullet" vs "cartridge" or "grip" vs "stocks".
And is it "grip" or "grips"? I've heard (and used) both. It's one thing with two pieces.