KABOOM: 300BLK fired in a 5.56 FS2000

Alex C.
by Alex C.

I guess the good part about 300blk is that it uses the same bolt and magazines as a .223/5.56, but the bad part is that is uses the same bolt and magazines as .223/5.56. This happened 12/17/2013 when I was at the range with a buddy doing some recreational shooting.

Pictured is is my friend’s .223 FS2000 that he accidentally shot a 300blk round through. This was his first time shooting the gun. He is an avid reloader and a big fan of both 5.56 and 300blk, so one could see how a round or a magazine may have gotten swapped by accident. When he pulled the trigger a very strange noise could be heard and smoke started billowing out of the gun’s trap door behind the picatinny rail and the bolt seized. The case blew out into the bolt face so hard that we were not able to remove it.

I was wondering to myself how the round even chambered and it is quite simple. Reloaders make 300blk by cutting the neck off of a .223 case and resizing/necking it down to accept a .30 caliber bullet. The projectile used was a very short and lightweight bullet (125 or 130 grain) with no jacket on the rear. I assume that this allowed the bullet to fit in the chamber, and when it was fired I imagine the projectile expanded to be three inches or so.

When a bullpup catastrophically fails, it can be quite terrible because the action is right next to the shooter’s face. The fact that the gun did not explode and injure my friend I believe is a testament to FN’s quality of materials, especially their legendary cold hammer forged barrels. We inspected the gun and could find nothing out of the ordinary:

However the firearm no longer functions as the extracted rounds will not properly enter the ejection chute that is parallel to the barrel.

So 300blk fans, be careful and make sure this doesn’t happen to you. It could result in a broken gun, or serious injury.

Alex C.
Alex C.

Alex is a Senior Writer for The Firearm Blog and Director of TFBTV.

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  • Freebug Freebug on Dec 21, 2013

    How the heck is this even possible? The 300BLK will not chamber into a 5.56 one. I know, because its happened to me.

    • Sprky777 Sprky777 on Sep 01, 2014

      @Freebug Is it possible for the bullet to be jammed back into the case when it hits the smaller chamber?

  • Brandon Brandon on Oct 15, 2014

    I have a Glock 20 and a .40SW conversion barrel; so when I go to the range I always double check which barrel is in and which caliber is loaded. I would have thought .300BLK would be easier to distinguish from 5.56 as opposed to 10mm from .40 :/