Wall to Wall: Testing Penetration of Home-Defense Ammo

“Which gun and what ammo should I use for self-defense in my home?” is one of the most common questions students ask during home-defense classes. The simplest answer is to use the firearm with which you are the most comfortable. Use the gun with which you train regularly and with which you are most proficient.

The more complex answer involves taking into consideration the ability of different rounds to penetrate interior and exterior walls. The calculation of which gun and ammo to use varies with each individual’s situation, including everything from where the person lives to the layout of his or her home. And one should consider the proximity of his or her neighbors, where people are likely to be in the house, the likely paths of illegal entry, the resident’s skills, and the building materials likely to be hit by any errant rounds.

Many people suggest a .22 rifle or pistol or 20-gauge birdshot if you live in a situation with few intervening walls between your likely points of defense and another person’s living space, such as in an apartment. Likewise, I also often hear about the importance of using defensive rounds over “ball,” or fully jacketed practice ammo, reiterated in such classes. I have heard many instructors (and I will admit I am guilty of this too) approximating answers to interior-wall-penetration questions. I have often generalized that one or two interior walls will stop birdshot or .22 LR and three to four walls will stop 9mm.

The question is, however, whether these estimates are correct, and the only way to find out was to put them to the test.

Home-Defense Ammo Testing Methods

Data such as power factor, which incorporates the round’s weight (grains) and velocity (feet per second), can provide a guide to estimate which rounds may be more or less penetrative. For instance, almost all civilian defensive rounds will likely be stopped by concrete or brick walls — regardless of velocity and weight. However, common interior walls are made of particle board, paneling and sheetrock. None of these building materials are initially going to stop a bullet. And a round may penetrate many such barriers (dependent on the power factor of that round). Thus, if the person is worried about penetrating interior walls in a home-defense situation, he or she can assume that lower-power-factor rounds (less penetration) would be preferred to higher ones (more penetration).

Almost all civilian defensive rounds will likely be stopped by concrete or brick walls — regardless of velocity and weight.

The penetration tests I conducted were aimed at adding objectively measured data of interior walls to these estimates, with the goal of giving those making home-defense calculations as much information as possible. Hardcover books were used as a cheap source of “hardening” interior walls from concealment to cover — meaning a surface that can stop incoming rounds rather than simply conceal a person’s location. There are multiple online videos showcasing such books stopping incoming rounds, and such sources have suggested using a few hardcover books to make soft interior walls less penetrable. I also tested the usefulness of this technique.

Materials for Testing Ammo

I tested a variety of handgun rounds ranging from .22 LR up through 9mm (FMJ and defensive), .357 Magnum, .40 S&W, 10mm and .45 ACP (FMJ and defensive). For the shotguns, I used 20- and 12-gauge birdshot and buckshot, and for the AR-15, 5.56 NATO. Each round was fired into a custom-built sheetrock rack at a distance of 7 feet. I chose this distance to simulate defending an average-sized room in a residential house or apartment. Barrel lengths were kept as consistent as possible at approximately 4 inches for the handguns (sticking with full-frame Glocks where possible), 22 inches for the shotguns (both Remington 870s) and 16 inches for the AR-15.

The sheetrock was in a 10-foot-long rack comprised of two-by-four spacers to simulate interior walls. In total, there were 24 half-inch sheetrock panels, each measuring 16 by 16 inches and each separated by 3.5 inches. This was chosen to allow each two panels to simulate a wall. Each round was fired multiple times and checked for consistent penetration results (rounds that either consistently penetrated the same number of panels or at most plus or minus one panel). Though these tests did not include intervening spaces (rooms) between the “walls,” they did provide a guide for how many half-inch sheetrock panels were needed to stop each round.

The Hard Numbers

First, several experienced firearms instructors present during the tests underestimated how many sheets it would take to stop both the 20-gauge birdshot and the .22 LR. Second, except for the 5.56, there was little distortion of the bullets (both FMJ and defensive) as they penetrated the layers of sheetrock before finally stopping. The 5.56 bullets were noticeably flattened. And the largest holes relative to the size of the bullets were the 5.56 and .45 ACP, as both rounds likely started to tumble as they penetrated successive layers.

Each firearm and cartridge used is listed as well as if the test utilized practice FMJ or defensive rounds. The specific ammunition used, the grain of the bullet and the published average feet per second are also included. The last two columns contain the results of the penetration tests. “Penetration” is the number of sheets of half-inch sheetrock that the rounds fully penetrated; this number can be divided by two to get the number of “walls” penetrated. The last column lists whether two hardcover books sandwiched between two half-inch sheetrock panels (filling the 3.5-inch space) stopped the tested round (yes or no).

Penetration Results

Generally, all rounds tested were easily able to penetrate multiple walls’ worth of intervening barriers. Even 20-gauge birdshot fully penetrated six panels (the equivalent of three sequential interior walls). Though still not ideal, the data collected would support the use of shotguns or .22 LRs if there is a high concern for interior penetration (as these ranged from six to 10 panels penetrated). Those defensive rounds tested were less penetrative but tended to not “flower” as they penetrated each layer of sheetrock. Handgun rounds (9mm and .45 ACP) all penetrated at least six walls of sheetrock and, in the case of 10mm, over 10 walls.

Though the 5.56 bullets showed the most deformation, they were also terribly penetrative (19 panels, or nine walls) and, beyond the first two or three panels, created relatively large holes as they tumbled along their paths.

Something With Which to Work

Clearly, every individual will have a unique set of concerns regarding his or her home-defense choices, but hopefully these tests provide an objective view of penetration of various rounds. Like all attempts at being objective, the desire to hold all other variables equal (barrel length, distance from first panel, same thickness and same material for each panel, and each panel the same distance from each other) results in comparable data but at a cost of realism (walls of differing materials, intervening spaces, furnishings, etc.). Thus, these results are provided as simply an additional metric with which you can make informed decisions.

---

Weighing Your Options … Prioritizing Your Home-Defense Loadout

Before anyone has an aneurysm from the rage he or she is feeling toward Mr. Nadler “suggesting that we use a .22 for home defense,” let’s all remember the two most important factors in home-defense gun use.

First, it will be more important that you have a gun when you need one than what kind of specific gun it is. This is and always will be the fundamental tenet of home defense. I know you like 12-gauge shotguns, and so do I. But what works best for you and me might not work best for everyone else.

Second, when a lot of contemplative gun owners talk about “over-penetration,” they’re not actually talking about over-penetration in the context of shooting an attacker. They’re really talking about a home-defense shooter not hitting his or her target. Before you start worrying too much about whether a round sent from your home-defense firearm will “penetrate too much,” worry about whether you’re good at hitting that at which you’re shooting. I can count on one hand the number of times I’ve even heard about an innocent person being injured by rounds that had passed through an assailant and then struck said innocent party. Those aren’t the rounds that injure innocent bystanders. The rounds that injure innocent bystanders are the rounds that don’t hit their intended targets.

There is not a firearm cartridge that will stop an impending, unavoidable threat of death or great bodily harm that will not also penetrate multiple layers of standard building materials. This is the reality in which we have to operate. Sure … it’s important that you take over-penetration into account in the context of home defense. But there’s no reason to abandon your preferred sidearm or shotgun just because it goes through drywall.

— Ed Combs, Senior Editor

Related:

What Happens If You Miss? Home-Defense Caliber Comparison
How to Properly Store Ammo