It refers to a condition of older firearms and the danger when they are mis-handled, sometimes leading to accidental discharge...(I hope that's close...I did not Google it)
   Therefore the expression refers to humans "shooting off their mouth" or responding to a situation with inadequate information....and I'm sure that is what Kendall meant, being proficient in firearms himself.

I just hate to see every use of 'cock', whether in firearms or fowl, made into a naught pun....it reduces the effect of GOOD puns and wordplay on the subject.