223/556 and the AR15 Barrel

In the world of the AR15, shorter is cooler.  This runs contrary to everything else in life.  Guys want giant trucks, giant houses, giant dogs, big big big!  Even in firearm calibers there are those that would rather have giant calibers such as 458 SOCOM or 50 Beowulf.  Yet when it comes to the AR15 it seems that the opposite holds true or should I say, the opposite holds false  - The AR15 is something where size actually does matter either in a bigger caliber or a longer barrel.

The original M16/AR15 had a 20 inch barrel.  With the 55grain rounds of the time they would achieve a muzzle velocity of 3259 feet per second.  It was determined at the rifle’s conception that a velocity no less than 3000 feet per second would be needed to achieve fragmentation and thus maximum lethality in the 55grain M193 round.

During the Vietnam conflict Special Operation Groups or SOG Teams would conduct clandestine operations in Vietnam ranging from black propaganda to direct action.  A shorter, handier rifle was developed to lighten the load and compensate for SOG’s long term reconnaissance patrols and for rear echelon troops not needing a full rifle.  The new M4 Carbine had a barrel length of roughly 14.5” giving a muzzle velocity just a touch over the needed 3000 ft/s.  This meant that the M4 could rarely have the needed velocity past 100 meter mark to achieve the lethality that the round was developed for.  With this limitation a new round was developed.  The slower moving but longer 62 grain round designated the SS109 was a fair way to fix some of the fragmentation problems.  It may seem counter intuitive, but the longer SS109 (although slower) would fragment easier as it was a longer bullet.  Think of it as trying to break a short stick and trying to break a longer stick – the longer acts as a better lever and snaps easier.

So the M4 was…. Well….. better now that it had a new round but after the battle of Mogadishu, Delta reported that their M4 carbines had little effect on the Somalis.  They often switched to their heavy hitting 1911s to bring the insurgents down.  It was forgotten that simply having a longer barrel on the M4 would of given them back the lethality that their rifles needed.

USSOCOM found that the higher unlock pressures generated by the shorter M4 gas system, caused premature wear on the rifle causing parts needing to be replaced or repaired at a rate 4 times faster then that of the M16.  For a government agency it is not a big issue… for an individual on a budget, this seems like a big deal.

But for reasons I simply can’t understand the mentality of “smaller is cooler” concept took the AR15 platform in a ridiculous direction; 10” and 7.5” AR15 barrel lengths.   Essentially if you were to stick the barrel of such an AR against someone’s flesh, you MIGHT get lethal bullet velocity but I would argue the blast is more effective at that point in dealing damage.  10” AR15s simply turn bullets into noise.  There is no advantage at that point other than LCF – Look Cool Factor.  If you really need something that short, switch to a SMG or a pistol caliber carbine.

The main people I deal with are not military and don’t have milspec M193 or SS109 and are using the similar (but not identical) .223 Remmington round.  I can only conclude that the minimum length for the lower pressure and lower velocity 55gr .223 Remington, a barrel length should be no less than 18 inches to get the needed effect out of the round.  Should a user opt for a heavier 62gr bullet, you could go as short as 16”.  But always remember – bigger is better.