"I think we have to look at the fact that we lose 90 people a day from gun violence. This has gone on too long and it's time the entire country stood up against the NRA."
-- Hillary Clinton

U.S. Army standard-issue M4A1 carbine. This is an "assault rifle." Image source: U.S. Army.

In one of the few big surprises in this week's first Democratic Presidential Primary debates, former Secretary of State Hillary Clinton blasted Senator Bernie Sanders' record on gun control. Sen. Sanders is on record as being in favor of banning assault weapons, but he also voted multiple times against passage of the Brady Bill, a federal law that mandated federal background checks on firearms purchases, imposed waiting periods before a gun sale could occur, and restricted certain people's rights to own firearms, period.

Clinton attacked the senator for these votes this week. She used some questionable facts in doing so, conflating more numerous suicides with murders to arrive at the "90 people a day" figure, for example. But the argument was at least defensible, and it captured the mood of a nation that's mad as hell about gun violence -- and is not going to take it anymore.

But what will Washington do about it?

Defining terms
Let's start with the hot-button issue of the day: "Assault rifles," often referred to generically as "assault weapons." Rifle-size assault weapons played a role in the mass shootings at Columbine in 1999, at Sandy Hook Elementary School and in Aurora, Colorado, in 2012, and most recently, in the shootings at Umpqua Community College in Oregon.

Critics say such assault weapons should be banned outright, and with them, high-capacity magazines and certain types of bullets. But while most people agree about what "high capacity" means -- magazines holding more than 10 rounds -- and while bullet calibers can be calculated down to three decimal points, the definition of an "assault weapon" seems very much in contention.

What is an assault rifle?
According to popular pro-gun website assaultweapon.info, critics of assault rifles don't always know what they're talking about. According to this website, an assault rifle has a very specific definition: It's a military-grade machine gun such as an M4A1 carbine (pictured above), which can fire both semiautomatically (pull the trigger once, one bullet comes out), or automatically (pull the trigger once, and the weapon keeps firing till empty).

Except for some very limited instances, the sale or purchase of such a machine gun is illegal in the United States -- and has been since 1986.

This XM-15 carbine, in contrast, is not an assault rifle -- but you might not know from looking at it. Image source: Bushmaster Firearms International.

What is not an assault rifle?
In contrast, weapons that resemble assault rifles cosmetically, but are incapable of full-automatic firing, have, since 1989, been dubbed "assault weapons." In the U.S., this class of firearm includes such semiautomatic rifles as the AR-15, and also certain AK-47 variants.

The Wall Street Journal once summed up the difference pretty pithily: So-called assault weapons "look like machine guns, but they do not function like machine guns." Rather, they "function like every other normal firearm -- they fire only one bullet each time the trigger is pressed."

A distinction with one crucial difference
Other advocates of tighter gun control, such as the PublicHealthWatch blog, point out that the high-muzzle velocity makes even non-assault-rifle assault weapons more dangerous than other semiautomatic firearms, and deserving of regulation.

Citing data from gun manufacturer Sturm, Ruger (NYSE:RGR), PHW notes that "the popular Remington brand .22 Rimfire ammunition commonly used [in semiautomatic hunting rifles] has a muzzle velocity between 700 and 2,000 feet per second." In contrast: ".223 ammunition most often used by the AR-15 assault weapon ... can achieve a velocity of 4,000 feet per second. Some AR-15s are designed to accept 5.56 NATO ammunition, a similar round to the .223 that has a velocity of up to 3,130 feet per second." PHW goes on to describe how higher-velocity rounds fired from assault weapons cause more damage to the human body than lower-velocity rounds fired from other semiautomatic rifles.

Moreover, argues gun control advocate the Violence Policy Center, due largely to their similar appearance to true assault rifles, assault weapons should be easier to regulate than handguns, for example. This is because assault weapons' "menacing looks, coupled with the public's confusion over fully automatic machine guns versus semi-automatic assault weapons ... increase the chance of public support for restrictions on these weapons."

And judging from the comments being voiced at this week's debate, certain candidates for president intend to push for tighter restrictions on assault weapons.

Smith & Wesson Model MYP15. Image source: Smith & Wesson.

What does it mean to investors?
Believe it or not, after watching the Obama administration make only halfhearted attempts to tighten restrictions on firearms for the past seven years, we're now looking at yet another contest for the White House in which gun control will stand center stage. And once again, we'll likely see gun owners stampeding to the gun store to stock up on guns 'n' ammo "before they ban them."

Chances are, this upcoming gun-ban threat will prove just as hollow as the ones preceding the 2008 and 2012 elections. But that won't make any difference for investors. We're likely about to see the stock prices of gun manufacturers soar once more, tracking greater gun sales. But which gun manufacturers in particular? Who is it that makes these assault rifles, assault weapons -- whatever you want to call them -- anyway?

Round up the usual suspects
It's almost easier to tell you who doesn't make them. Sturm, Ruger, Smith & Wesson (NASDAQ:AOBC), and even privately owned Bushmaster all make various versions of the AR-15 "assault rifle." As noted above, these semiautomatic firearms aren't really assault rifles at all -- but that won't allay fears that a new president will try to ban them.

Sturm, Ruger and Smith & Wesson, being the only two "gun stocks" publicly traded in the U.S., are the two most obvious beneficiaries of a renewed Election 2016 gun-ban scare. Both Sturm, Ruger and Smith & Wesson make AR-15 variants that fit the popular conception of what an assault weapon looks like -- even if their guns are not technically assault rifles.

If you saw this week's debate, and believe that a renewed push for an assault-weapons ban will soon be in the offing, these are the two stocks you should be looking to buy today.

Ruger's SR-556 carbine is another semiautomatic "assault rifle" that will soon be in gun regulation activists' crosshairs. Image source: Sturm, Ruger.