Shameless pedantry.

PEDANTRY BEGINS.
In gun terms, a magazine is not a clip.  A magazine is the container for the cartridges, shells, or other projectiles and is loaded into the firearm prior to usage.  A clip is a piece of metal that is used to hold cartridges in place to either load them directly into a firearm or into a magazine; it may of may not be inserted directly into the firearm, as is the case for an M1 Garand, but if pops out once the cartridges have been loaded.  Magazines are vital to the operation of a firearm, whereas clips are helpful but not vital.
PEDANTRY ENDS.
That said, I'm still going to use "clip" as a term for a gun's magazine.  Screw the grammar, I have artistic license!