Well the term "killing power" is pretty subjective. you are comparing apples to oranges with a bow and a gun, they both kill in totally different ways. You aren't going to put an animal down in its tracks with a bow unless you spine it, where as "bang-flops" with a gun are fairly common.A well placed, razor sharp arrow in the vitals is a very efficient killer though. If you define "killing power" as the ability to kill at different angles and distances a gun wins hands down. With a bow you have to wait for a fairly close broadside or quartering away shot. With a gun you can take ethical shots at much longer ranges, and you can also take them with the animal straight on, quartering towards you, and even in the neck.