FN 5.7 Information & Cautions
By Andrew Jarvis
Jarvis Inc.
http://www.jarvis-custom.com/contact-us/
The FN 5.7×28 pistol is a delayed blow back, light recoiling handgun of a weight that makes it very attractive as a duty or carry weapon. Fully loaded the handgun weighs 1.6 lbs. This pistol, with a full magazine and two full spare magazines weighs less than a fully loaded steel frame double action 9mm pistol without any spare magazines.
There are currently three models in service; the IOM, USG, and MK2. Variations in the three, except for the very first IOM models are very similar. Polymer materials are used for both the frame and as a covering for the steel slide. Current models are single action and have a concealed hammer. Other differences not withstanding sights and magazine release are primarily cosmetic.
Factory ammunition for the civilian market is either FN 28gr JHP SS195 or the FN 40gr FMG SS197. An alternative to the FN loaded ammunition would be the Federal 5.7 round designated AE5728A. (See factory issued information sheet below)
There have been numerous accidents stemming from the use of reloaded 5.7×28 ammunition. This has resulted in us assuming the same position as the FN factory regarding the use of reloaded ammunition. Using any ammunition other than what was listed previously can result in a catastrophic accident.
When the pistol fires, the thin case neck expands (as intended) and tightly grips the wall of the chamber and seals the chamber against the escape of gas to the rear. At the same time the thicker rear portion of the case and case head elongate and sharply strike the breech face (the slide), which initiates the slides rearward movement. The slide and case head continue to move backwards leaving the case neck tightly stuck to the chamber wall. The sticking of the case neck to the chamber wall is overcome by the lubricant that is applied to all factory 5.7×28 cases. This lubricant allows the case neck to break free and eject from the chamber. This approach is no different than the lubrication of cases in machine guns and auto rifles decades ago. When the 5.7×28 ammunition is fired, and often cleaned after being fired for reloading, most (if not all) of the lubricant is removed. When the cases are then reloaded, they can stick to the chamber wall to the point of case rupture, resulting in catastrophic failure of the gun and possible injury to the shooter.
Another concern is the case offset after firing. According to Western Powders, Inc., the pressure required to resize the case for the FN 5.7 is close to twice that of any other round. This information leads us at Jarvis, Inc. to believe that the FN 5.7 round was never intended to be reloaded. The following page is a warning sent to us from FN regarding their attitude and concerns towards reloaded 5.7 ammunition.
