Several years ago, I worked for a large scientific organization that was right down the road from the local gun range. We used to shoot a lot of stuff on the lunch hour and after hours. I have some observations that may be useful to the self-defense shooter, home defender and others in terms of cover from a materials standpoint.
First, the destructive power of a round is proportional to its velocity. The more you can slow a bullet down, the less damage it can do and the less range it has. And the more you can flatten a bullet, the faster it slows down. Finally, the more you can break a bullet apart, the less damage it may do. The goal in finding cover is for the material you are behind to break the bullet into smaller pieces. It’s easier for the individual parts to be stopped. If you can get the parts below 400 feet-per-second, odds are good they will not break the skin.
What Stops or Slows Down Bullets?
Materials tested include metal, fibers, stone and liquids. One or a combination of any of the four may work. It depends on your application. Obviously, in a gunfight you’ll simply be looking for something to get behind. If you can remember what has the best stopping power, however, you’ll be able to find safer cover. These materials may be better kept in mind for constructing a safe room or dry-fire practice area.
Wood is terrible at stopping bullets. Woven Kevlar works great. Fiberglass is so-so. Several layers of fiberglass with the right epoxy can be great!
Stone and liquid stone (concrete) work great! But they are not very portable. They have thickness issues. “Baby” stones like pea gravel or sand have their place. Ceramics also fit here.
These are great for the thickness. Hard steel works best. Soft steel comes next, followed by aluminum (hard and soft are blurred) and then copper. We used to shoot a lot of large electrical transformers. It was quite educational. They are layers of copper windings and mild steel. Electronics soak up a lot of bullets even from high powered rifles.
The Importance of Layers When it Comes to Cover
This leads us to a very important point: layers! Combined layers can stop more effectively than a single layer of the same thickness. Four 1/16-inch-thick sheets can stop more than a single 1/4-inch sheet. Some of the layers may be breached, but the overall thickness has not. It may be hard for somebody to work with a single thick layer of steel but not smaller layers. It normally takes between a 1/4 inch to a 1/2 inch of steel or 3/8 inch to 3/4 inch of aluminum to stop a bullet. Something like a metal target needs to be one solid layer, as does an active backstop. However, something like a safe room or dry-fire station can use layers.
Stones are great at breaking up bullets. Patio blocks or even bathroom tiles can break up bullets. The problem is that they often break up along with the bullet. You may want to set them or glue them to some sort of backer like plywood to help hold them together. Think outside of a safe room. Works great but is one use only.
Wood and other fibers: Wood is the most common and easiest for most people to work with. It is crap for stopping bullets. I have layered as many as three 3/4-inch sheets of plywood and bullets still fly through. That is thicker than most wall studs by 50 percent. Here is why it is VERY useful. It soaks up shrapnel like a sponge. You can use it to help prevent bounce back. Now, if you were to glue some 1/8-inch sheets of steel between those layers of plywood, then you really might have something.