I say the old barbaric ways were pretty effective. I mean, if you murder someone, do a drive by shooting, armed robberies, rape, basically any violent crime, and you get caught and found guilty, you die. First time, every time.

Then you don't have to mess with the honest gun bearing folk anymore.
You send them to jail, and a mere one out of a thousand actually comes out with a straight attitude. Most go and do something stupid again, this time "educated" by smarter criminals then themselves,

and we pay to house and feed them all over again.
Price of a .308 round, about 50¢ or so. (my personal favorite due to the message it sends to other scum)
Price of electrocution, what a couple bucks in electricity?
Who knows what gas chambers and lethal injection cost. But I'd wager it's fairly cheap too.
How much do you think it costs to feed and house them for 5 or 20 years?