Full Metal Jacket (FMJ) Bullets Explained
The full metal jacket bullet is probably something you have in your house right now. This is an extremely common bullet type that is mostly used for target shooting at ranges or in your backyard. The term full metal jacket means the lead bullet is encased in another, harder metal. This is typically copper but can sometimes be other materials and even hybrid composites instead. The manufacturer of the FMJ bullet can have a huge variety of ammo lines using their proprietary creation methods so you can usually pick and choose from different materials, styles and uses.
Full metal jacket bullets can also be called a few other things like full metal case or have additional suffixes like “boat tail” to let you know right away what the intended use of the bullet it or how it will perform. Some common types are the full metal jacket boat tail, full metal jacket flat nose and full metal jacket truncated cone. Each of these is tailored for a specific use but retains the basic properties of all FMJ type bullets in regards to the lead.
The number one perk to using a FMJ bullet is that the lead bullet is mostly or even fully surrounded by copper or another metal. This helps prevent lead from the core of the bullet from depositing itself in the barrel as it is fired. Although not a major issue for the casual shooter and hunter who may fire 100 rounds between cleaning, the high volume shooter the FMJ bullet is a huge advantage. As a lead bullet engages the rifling of the barrel, a small amount of lead is left behind. Over several shots, this lead will build up and make the shots less accurate. With a jacket over the core, the depositing of metal is greatly reduced, this allows more shots to be fired before accuracy degrades.
The FMJ bullet was designed in the late 1800's for use in military rifles. Not long after this, the Hague Convention of 1899 made the use of bullets that easily expand or flatten inside the body illegal. Interestingly enough, the United States did not sign off on this. The agreement held that the bullets used by the signatories could not open upon impact, such as hollow points. This is because the FMJ bullets were likely to cause a "through and through" wound instead of mushrooming and causing a more grievous wound. For the civilian shooter, this means that care must be taken when using FMJ bullets as they can easily penetrate humans and whatever is behind them.
FMJ bullets perform very well ballistically and you won’t be losing accuracy or speed if you decide to put some through your weapons. The full metal jacket bullet type is extremely popular and every major manufacturer sells an assortment of it. Just keep in mind what you’re going to be using it for when choosing the line of ammunition you’re going to get.
Some regions don’t allow FMJ bullets at all on public lands unless they are total metal jacketed so double check before you load up and head out.