Phoenix, AZ may be the best comparison for high gun ownership and low crime. Granted, the Phoenix metro is about 12x larger than DC, but (my perception when I lived there)firearms ownership is high, and the regulations are very very free. For example, open carry is allowed, no permit required, anywhere in the state. concealed carry requires a permit, but it's a 'shall issue' state, and IIRC the only req to get a concealed carry permit is to pay the money and not be a felon. No course, no range time.
www.disastercenter.com has information on crime rates. Phoenix Metro has a population of 6.2 million, a violent crime rate of 513 per 100k, and a murder rate of 8.4 per 100k. DC has a pop of 550k, a violent crime rate of 1459 per 100k, and a murder rate of 35.4 per 100k. If you remove the outlying cities from metro Phoenix, and just use the main city, the pop is 1.5 mil and the murder rate is 15 per 100k. and the perception as a resident of phoenix is that everyone is armed.
A little more detail: I've taken the data at www.disastercenter.com for DC crime rates and population (which at least at first glance don't seem obviously wrong, but I'm not sure where the data came from for some years), and converted it to rates per 100,000 people.
The following data will tell you how successful the 1976 law was.
Murder rate in 1976: 26.78/100,000; in 2005, 35.42/100,000.
Now, it is true that robbery rates have fallen substantially over that period of time from 1003.42 to 672.09--but after a dramatic spike in the years after following the 1976 law as high as 1635.06 in 1981.
Aggravated assault rate in 1976: 378.77. In 2005, 721.32--almost twice as high.
Burglary rates are MUCH lower than they were in 1976--but again, after an astonishing spike in the years after the law took effect. If you want to give credit for today's lower burglary rates to the gun law, then you have to ask why it took twenty years for rates to drop, and stay down.
Ditto for larceny-theft rates--it took more than twenty years for the rate to drop below the 1976 level.
Vehicle theft rates went from 420.51 in 1976 to 1402.31 in 2005--more than tripling.
What's really interesting, however, is comparing 1960 to 1976--you know, not only before the 1976 gun law, but the 1972 mandatory registration law, and the 1968 Gun Control Act (which made it illegal for DC residents to buy guns in adjoining states, or to buy long guns mail order).
With the exception of aggravated assault and vehicle theft, which were just slightly lower in 1960, the difference is astonishing. DC was almost a civilized place to live. 10 murders/100,000; 140.32 robberies/100,000; and so on for the other crimes.
I'll figure out how to produce some images to put up tomorrow.