The primary definition of “gun” is: “a weapon incorporating a metal tube from which bullets, shells, or other missiles are propelled by explosive force, typically making a characteristic loud, sharp noise.”
The primary definition of a “weapon” is: “a thing designed or used for inflicting bodily harm or physical damage.”
The one time a weapon -- a sword which is "a 'weapon' with a long metal blade and a hilt with a hand guard -- was wielded in Jesus’ presence, he clearly demanded, “Stop, no more of this!”
Before receiving absolution, the penitent resolves “to sin no more and to void the near occasion of sin.” By its very definition, a gun is not only a near occasion of sin; a gun is an outright invitation to sin.
Christians are called to be peacemakers. Peace is not "propelled by explosive force."
"They shall beat their swords into plowshares, and their spears into pruning hooks; one nation shall not raise th sword against another, nor shall they train for war again." (Is. 2:4)