Under the National Firearms Act, certain types of weaponry are very heavily regulated. For example, when it comes to fully automatic weapons -- guns that spray bullets when you hold the trigger down -- civilians are limited to guns that were in circulation as of 1986, must register their weapons, and must pay a $200 tax. Given the tax, the limited supply, the paperwork wait times, and the legal hassles, machine gunning is a very expensive hobby, but it's grown in popularity anyway.

NFA restrictions also apply to suppressors, short-barreled rifles and shotguns, "destructive devices" like grenades, etc. Our update today features a report from the Bureau of Alcohol, Tobacco, Firearms, and Explosives with some new data on these weapons and accessories.

Of special interest is the Form 4, which is what civilians fill out when they transfer an NFA-regulated item. I was surprised to see that the ATF processed even more of these forms in 2013 than it had in 2012:

There's a similar trend in the Form 1, used to make NFA items without a license. Making a machine gun for civilian use is prohibited, but Form 1 is used, for example, by those who want to build their own suppressors or short-barreled rifles or shotguns:

Robert VerBruggen is editor of RealClearPolicy. Twitter: @RAVerBruggen