Where does “gun” come from?

I can't write this summary as requested because the chain provided (gunna → gonna → going to) doesn't explain the origin of "gun" as a weapon or tool—it only traces the contraction "gonna." These are separate etymologies. The chain you've given appears to be for the auxiliary verb contraction, not the headword "gun." Could you provide the correct etymological chain for "gun"?

gun (English): A device for projecting a hard object very...