What Is The Difference Between A Jacketed And Unjacketed Bullet?
What Is A Full Metal Jacket Bullet
Full Metal Jacket (FMJ) bullets refer to small-arms projectiles made of a soft core interior (usually this is lead), and a harder encased shell. The shell, or “jacket,” is commonly made of cupronickel, gliding metal or a steel alloy of some kind. Sometimes this metal coating is a hybrid composite material. It is better on the bore, leaving less metal behind and preventing as much damage as possible during fire. They were invented in the late 1800s. The FMJ was originally developed for the Swiss Federal Ammunition Factory and Research Center by Swiss Colonel Eduard Rubin.1These rounds were designed specifically to withstand deformation and improve the feeding characteristics of the mechanical manipulation of the cartridge.2Sometimes FMJ rounds are called “full metal case” bullets. Some of the most common types of FMJ rounds include: full metal jacket boat tail, full metal jacket flat nose, and full metal jacket truncated cone. Although all of these rounds share similar FMJ characteristics, they are all intended for very specific, and different uses.3
Differences between Full Metal Jacket Bullets and Unjacketed Bullets
Unjacketed bullets are typically purely lead in construct. Full Metal Jacket bullets are simply lead bullets coated in copper and/or steel alloy. One of the major differences between lead-only bullets and FMJ bullets is the higher muzzle velocity of the FMJ bullet. Essentially, jacketed bullets are stronger, allowing for less impact-absorption, which means more of the blast energy is transferred into muzzle velocity. FMJ bullets may provide a significant advantage when engaging a target behind cover, it does often mean completely piercing a target and failing to disable it. It can also lead to undesired collateral damage as the bullets pass through the target (check out some more on barrier penetration). In other words, FMJ rounds are less expansive in soft tissue. Ballistically speaking, the FMJ performs well with little loss in accuracy.
Lead is a very soft metal and often leaves deposits behind in the barrel. Having a FMJ can create enough of a hard shell that little to no metal is left behind in the barrel. This actually has a positive impact on the accuracy of the bullet as well. It may only be an advantage truly noticed by a high-volume shooter, it is nonetheless better for the gun all-around.
Last Words on Full Metal Jacket Bullets
Full Metal Jacket rounds have less capacity to expand when compared to a normal lead round or a hollow point bullet. As mentioned, this may create less wounding and lead to less stopping power. Using FMJ rounds for home defense is ill-advised as it can be dangerous to civilians in (and outside of) the home. Jacketed Hollow Points (JHP) are worth mentioning, as they combine the concepts of hollow point rounds and FMJ rounds. Hollow points have a hollowed out front center, creating a deformed impact zone, mangling a giant hole in soft tissue. In short, JHP rounds can be devastating to soft tissue. There are also normal hollow point rounds, which are also worth reading about. Check out the difference between hollow points and regular bullets for more information.
Disclaimer: While many people wonder if Full Metal Jacket bullets are illegal, the truth is each region and locale is different. Always check federal, state, and local laws before purchasing or using FMJ rounds. And always shoot responsibly!
1Huon, Jean (1988). Military Rifle and Machine Gun Cartridges. Retrieved from: Ironside International.
2Wood, J. B. (2003). The Gun Digest Book of Firearms Assembly/Disassembly. Retrieved from: Centerfire Rifles, Volume 4 (2nd ed.).
3Ammo. Full Metal Jacket FMJ. Retrieved from: https://ammo.com/bullet-type/full-metal-jacket-fmj
About the Author:
Mark Doberman, The Proprietary Gun Smith
The Proprietary Gun Smith is a marksman, expert gun handler, ammunition specialist, survival guru, and lifetime gun enthusiast. He owns (or has owned) nearly every legal firearm and ballistic available, has fired nearly every gun, and regularly consults professionally in the firearm world. He has studied firearms and similar tactical lifestyle for more than 40 years. In addition to writing for ArmoryBay.com, TheProprietaryGunSmith has guest written for more than a dozen other sites and/or magazines in the industry.
How useful was this post?
Click on a star to rate it!
Average rating / 5. Vote count: