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What is a Bump Stock and How Does It Work?

What Is a Bump Stock And How Does It Work?

With reports that the Las Vegas shooter used bump stocks on several of his rifles, lots of people are wondering what a bump stock is. 

Now gun control supporters and lawmakers are talking about taking steps to regulate bump stocks. However, it’s probably safe to say that these are devices that the most people in the United States had never heard of until recently. With that in mind, it’s certainly worth it to have a discussion of just what the heck a bump stock is first.

Before we get started talking about bump stocks though, here is some useful background information to help put things in context.

As we discussed in a previous article, the National Firearms Act (NFA) of 1934 and the Firearms Owners Protection Act of 1986 placed very strict limits on the manufacture, transfer, and ownership of machine guns by civilians in the United States. Neither law amounted to an outright ban on machine guns, but they had the effect of significantly limiting the legal supply of machine guns that civilians could lawfully possess. For that reason, civilian owned machine guns are very rare and very expensive in the United States.

The NFA defines a “machine gun” as:

“Any weapon which shoots, is designed to shoot, or can be readily restored to shoot, automatically more than one shot, without manual reloading, by a single function of the trigger.”

Basically, any firearm that fires more than one shot each time the trigger is pulled is a machinegun according to the NFA. By the same token though, any firearm that only fires a single shot when the trigger is pulled (regardless of the actual rate of fire) is not a machinegun and is therefore not subject to those same stringent regulations. As a result, semi-automatic firearms are much more common and much less expensive.

With that in mind, shooters have developed several different techniques and devices to help achieve high rates of fire using semi-automatic firearms. One way of doing that is to “bump fire” a semi-automatic firearm.

Put simply, bump firing is when the shooter harnesses the recoil of the firearm to assist in rapidly pulling the trigger. When bump firing, the shooter exerts steady forward pressure on the stock with the support hand. The recoil produced by a firearm when it shoots pushes it backwards, but the shooter’s shoulder and the forward pressure on the stock “bump” it back forward until the trigger contacts the trigger finger. At this point, the firearm shoots again and starts the process over.

As you can see in the video below of the guy doing a bump fire demonstration, a shooter can achieve a pretty high rate of fire using this technique.

A really good three gun competitor can shoot 2-3 rounds a second with a semi-automatic rifle, which translates into a rate of fire of about 120-180 rounds per minute. The vast majority of people simply cannot squeeze the trigger much faster than that. However, a shooter can double that rate of fire when bump firing.

On the other hand, bump firing is not conducive to a high level of accuracy. Like you saw in the video, the guy was not cradling the rifle in his shoulder and did not have a firm grasp on the hand grip. Yeah, he shot a lot of rounds off very quickly, but it’s doubtful he’d be able to hit anything out past 25 yards or so when bump firing. 

In addition to the inherent inaccuracy of bump firing, it’s also a somewhat difficult technique to pull off because it requires a fair amount of strength and coordination. As a way of getting around these problems, some shooters designed a device we now know as a bump stock several years ago.

A bump stock operates under the basic same principles the guy was using while bump firing in the video above. The major difference though is that instead of bouncing back and forth off the shooter’s shoulder, a bump stock is designed to slide back and forth. This allows the shooter to exercise more control over the firearm.

As you can see in the promotional video below made by Slide Fire (a leading manufacturer of bump stocks), a bump stock is also relatively user friendly.

Now, accuracy is a relative term and is inversely related to rate of fire (the faster you shoot, the less accurate your shots normally are). So, while a firearm equipped with a bump stock will probably be more accurate than an off the shelf firearm simply being bump fired without a bump stock, neither is a poster boy for accurate shooting.

Regardless of what some people may say, no, a bump stock does not convert a semi-automatic rifle into an automatic weapon or turn it into a machinegun. It just enables the shooter to pull the trigger really fast and shoot a lot of rounds off in a short amount of time.

So, with all that being said the question remains: are bump stocks legal? In short, yes they are (as of October 2017).

Before they began selling bump stocks, the management at Slide Fire requested an evaluation of their product by the Obama Administration’s Bureau of Alcohol, Tomacco, Firearms, and Explosives (BATFE) in 2010 to ensure they should market their bump stocks without breaking the law. After evaluating the bump stock, the BATFE stated that a bump stock does not fit the criteria of a firearm part regulated under federal law and was legal to sell:

The stock has no automatically functioning mechanical parts or springs and performs no automatic mechanical function when installed. In order to use the installed device, the shooter must apply constant forward pressure with the non-shooting hand and constant rearward pressure with the shooting hand. Accordingly, we find that the ‘bump-stock’ is a firearm part and is not regulated as a firearm under Gun Control Act or the National Firearms Act.

Should bump stocks be banned? Well, that’s a question for another day.

However, if we’re going to have a debate regarding regulating bump stocks, you should at least know what a bump stock is and how it works first. If you’ve made it to this point in the article, I can guarantee that you know a whole lot more about bump stocks than the average person does.

Like what you see here? You can read more great hunting articles by John McAdams on his hunting blog. Follow him on Facebook The Big Game Hunting Blog or Twitter @TheBigGameHunt.


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What is a Bump Stock and How Does It Work?