Toward the conclusion of Brian Skiba’s new film, “Gunslingers,” there is a cliff-hanging moment that is, in its choreography and underhanded humor, worth sitting up for. During a tumultuous showdown between the good guys and the bad guys, a trio of cowboys from the former group find themselves on the gallows awaiting their comeuppance. When the trap door under their feet falls, gravity takes effect, the nooses gain in tautness, and our heroes struggle against certain death.