5.56, Short Barrels, and Fragmentation.

Every time I see a blog post or forum thread about a SBR/AR pistol in 5.56 in regards to self-defense, there are always the inevitable neighing naysayers who go out of their way to trying to prove to someone, anyone, that a short barreled 5.56 is not a good self-defense solution. They claim this, citing that short barreled 5.56's  (7.5"-12.5") do not generate the velocity needed to reliably cause fragmentation with the two most commonly available brass-cased 5.56 rounds; 55gr FMJ M193 and 62 FMJ M855. 2700 fps (feet per second) is the lowest 'threshold', if you will, at which these offerings are supposed to (meaning, maybe) reliably fragment and cause the desired effect on the target. Anything under that and it may, or may not. A 10.5" 5.56 will reach a MV (Muzzle Velocity) of around 2730-2750 fps with M193 and 2640-2760fps with M855. It then tapers off sharply to under the 'threshold'.

This is all correct information.

Having said that, most people who will be using an SBR/AR pistol for home defense are not subject to the rules that our Military must follow, such as those set after the Hague Convention. So, I ask you, why is this even being discussed? Why would it be considered, using ammunition may or may not work, when lives are at stake? Why would you not use something like Hornady T.A.P., Winchester PDX or Ranger, or Federal Hi-Shok? These are expanding bullets that allow all of their energy to be 'dumped' inside of the target and are designed to expand or 'fragment' at velocities down to 2000 fps and, in some cases, as low as 1700. The most common answers I have seen are:

1.     "I can't afford the self-defense ammo." Bullshit. You can pay the premiums for an SBR/AR pistol, but you can't afford 100-200 rounds of quality ammunition to test and then keep loaded to use when you and your family's lives are on the line?

2.     "I don't want to use hollowpoint/soft point ammo because I will be charged with murder/attempted murder." Regardless of what you shoot an intruder with, a good shoot is a good shoot and a bad one, bad. Only fire if absolutely necessary to prevent death or serious bodily harm, then shut the fuck up until your lawyer arrives.

3.     "Thet thare leetle peashootin' round is only for squirrels. Ain't nothin' better then' ma' .45!" This answer is one that I detest. It reeks of ignorance, and is complete pigeon religion. Here is why.

10.5" 5.56

• Hornady T.A.P 55gr @ 2740 fps generates 917 ft-lbs. kinetic energy. At 10 yds. it has 900 ft-lbs. of kinetic energy.
• 30 rounds available.

5" .45 ACP 

• Hornady Critical Defense 185gr @ 1000fps generates 411 ft-lbs. of kinetic energy. At 10 yds it has 404 ft-lbs. of kinetic energy.
• Assuming that "ma' .45!" is a 1911, most people will be limited to 8-10 rounds. A G21 will get you 3 more, and an FNX-45 will net you 15 total. 

Which would you choose presented with these facts?

Relying on fragmentation is dangerous, as there are other things besides velocity that can affect it. If an SBR/AR pistol is your HD weapon of choice, buy quality ammunition, test it in your lead dispenser, and train with it. Same goes for anything that you will use in life-and-death situation.

Be ready when the time comes, or suffer the consequences of your inaction.



Sources:

Velocity, Barrel Length
http://counterstrikefox.freeservers.com/mv.htm

http://www.sadefensejournal.com/wp/?p=1093&page=1

Velocity, Fragmentation
http://www.razoreye.net/mirror/ammo-oracle/AR15_com_Ammo_Oracle_Mirror.htm#velocity

Kinetic Energy calculator
http://www.shooterscalculator.com/bullet-kinetic-energy.php

For anyone who cares, here are the wound profiles of M855 and M193.

M855
http://www.firearmstactical.com/images/Wound%20Profiles/M855.jpg

M193
http://www.firearmstactical.com/images/Wound%20Profiles/M193.jpg