I cannot arrive to a conclusive interpretation of this poem, but I found it interesting nonetheless. I think the gun in this poem represents blind faith, because of how the gun is personified. The gun waits for its master, roams with its master, speaks for its master, and on being fired, smiles with “such cordial light.” The gun takes pride in serving its master, noting the fact that the foes of its master, will never “stir the second time,” implying that the gun never fails its duty. 

I can’t say for sure what Dickinson is trying to convey through the faithful personification of the gun. I’ll bullet some thoughts though.

• The Master is definitely male, so maybe the message involves female obedience, assuming the gun’s dialogue is representative of Dickinson herself.
• Or perhaps it is the opposite, the gun has the power to kill and will outlive its owner.