FN Five-Seven KABOOM

    Over at the Kifaru forum, “Fairchase” wrote that his FN Five-Seven fired a round out of battery, blowing it up and doing severe damage to his hand and thumb.

    Last week my FN Five-Seven blew up causing severe damage to my left hand (I am right handed). There are 6-8 pieces of shrapnel deep in my thumb and palm area which severed the nerves to my thumb and a portion of my palm. Surgery is required in an attempt to repair the hand by harvesting tissue from my leg. Wish me luck.

    The “explosion” occurred on the last round of a 30 round mag loaded with the factory 40gr v-max stuff. On this particular day I only had three loaded magazines (70 rounds total) with me for the Five-Seven but had several other handguns to shoot after the Five-Seven. I began with a 20 round mag loaded with hand loads, then a 20 round mag loaded with factory ammo and finished with the 30 round mag with factory ammo. It was the very last round of 5.7×28 in my immediate possession that ruined my day ……. and a whole lot more!!

    I have fired (600-700 rounds) both factory and hand loads through the pistol with zero issues since purchasing new in 2/2011. There are reports of the Five-Seven firing out of battery (OOB) which appears to be the case here but I am no weapons forensics expert. I am not a novice to shooting, handguns or reloading and have 20+ years of extensive experience with shooting and reloading.

    I have been completely straightforward with FNH (i.e. Browning) so will now wait and see how they respond.

    I have a lot of sympathy for Fairchase, but I think its more than likely that it was a handload that caused the kaboom. I would never recommend reloading the 5.7mm FN for use in pistols. The margin for error on a high-pressure and bottlenecked pistol round is a lot less than on an old “boring” cartridge like the the 9mm Luger. The maximum pressure of the FN 5.7×28mm is 50,040 psi vs. 34,084 psi for the 9mm Luger/Parabellum and 35,000 psi for the .40 S&W.

    Shooting Times once published an article about reloading the FN 5.7×28mm (since taken down, maybe for liability reasons). They listed a number of caveats for any would-be reloaders …

    There are a few things to keep in mind:

    • Using reloaded ammunition in PS90 and Five-seveN firearms voids any warranty and any liability of FNH USA. By choosing to reload, you accept full responsibility.

    • Because of its tiny case capacity, start at the listed minimums and work your way up in 0.1 grain increments.

    • Published load data varies greatly, so err on the conservative side. The min. and max. loads in the Western Powders manual are significantly higher than those listed in the new Lyman Reloading Handbook 49th Edition, which is what I used.

    • The 5.7×28 is very sensitive; adhere strictly to the loading data and COL guidelines.

    • Stick with flatbase bullets and Small Rifle primers. If you use Small Pistol primers, expect decreased performance.

    • Excessive muzzle blast and flash are to be expected with this cartridge.

    • FN- and Fiocchi-made ammunition both employ military-style, staked-in primers. You must ream the staking residue from the primer pocket before reloading.

    • Beware of hotrodding the 5.7×28. Though the 1:9-inch twist rate of the FNH USA guns might tempt a handloader to load heavy bullets, I highly recommend projectiles of 40 grains or less. Too-high pressures can be a real safety concern with the straight blowback PS90 and the delayed-blowback Five-seveN pistol.

    The maximum average pressure (MAP) for the 5.7×28 is 50,040 psi.

    [ Many thanks to John for emailing us the link. ]

    Steve Johnson

    I founded TFB in 2007 and over 10 years worked tirelessly, with the help of my team, to build it up into the largest gun blog online. I retired as Editor in Chief in 2017. During my decade at TFB I was fortunate to work with the most amazing talented writers and genuinely good people!