I've seen a few of this guy's youtube videos and while I've not done the research to verify his accuracy, his points are very compelling. Please watch this video and note that the lowest US murder rates were during the "war years" (WWII, Korea, Viet Nam) when many 18-25 year olds were in service (i.e., the age group most likely to commit murders) and that murder rates have dropped in the US (compared to the UK which has strict gun controls). Now this doesn't account for the weapon used, but the argument is worth considering.

Fireside Stats Chat - YouTube