After having several discussions with friends I did some research on the effective range of AR-15 rifles using various types of ammunition. In this post I'm going to discuss the maximum effective range of the most common bullet weight and type, 55gr full metal jacket (FMJ). As many people know the standard 55gr full metal jacket projectile's primary wounding capability comes from fragmentation. There is wounding performed by hydrostatic shock as well, and of course the path of the bullet. If a bullet itself hits a major blood vessel or vital organ it can of course be lethal. But when a bullet expands or fragments it greatly increases both the wound channel and the potential to damage something vital. It's a morbid topic, but if you use a firearm for hunting or defense, you want it to be effective, so it's an important discussion.
If a person chooses 55gr .223 or 5.56
NATO ammo for use in a defensive carbine it's important to fully
understand the fragmentation qualities and understand what the maximum
distance is at which a bullet fired from your rifle will still possess
fragmentation qualities. This is because it takes a fair bit of
velocity to give the bullet enough energy to fragment when it strikes a
target. Most experts suggest the necessary velocity to ensure reliable
fragmentation is 2700 fps. I've chosen this bullet for this discussion because by a large amount it's the most common bullet found in .223 and 5.56 ammo.
length is correlative to muzzle velocity. The shorter the barrel, the
lower the muzzle velocity. The shortest barrel seen in 5.56 rifles is
7", which is pretty stupid honestly. A large percentage of the powder
burns outside of the barrel and the velocity is way down when compared
against a standard length carbine. For purposes of this blog, we'll be
starting at a barrel length of 10.5", a popular length for short barrel
rifles used by military, police and civilians.
M193 (the military standard 55gr 5.56 cartridge) generates a velocity
around 2750 fps in a 10.5" barrel AR-15. This isn't much higher than
the fragmentation velocity. Since the bullet will be losing speed every
moment after it leaves the barrel, we can figure out it's going to drop
below the magic velocity threshold around 20 meters. That's not much
of a range at all. If you are using a 10.5" rifle for defensive use,
you'd likely be better off with a different type of bullet.
an aside, I'm using nice round numbers here, if you want to know exact
ranges you'll have to know your exact velocity out of your rifle. It
could easily be 50 fps plus or minus the average velocities listed here
which will change the range by a meter or ten.
move up to an 11.5" barrel we pick up a bit more velocity, 2875 fps or
so. It's a pretty nice bump from 10.5". It shows how a cartridge and
the burn rate of the powder chosen for factory loadings in that
cartridge is tuned to a specific barrel length. So by moving from a
10.5" to a 11.5" barrel we extend our fragmentation range out to 50
meters. This is a more useful range, but still very limited.
12.5" gets us to 2950 fps. This brings the range to 75 meters, still very limited.
gets us 3050. This is the barrel length used by the military in the
newest version of the M-16 rifle which is commonly called the M4. The
velocity increases are slowing down at this point, most of the powder
has burned by the time the bullet exits the barrel. This takes our
effective frag range to 100 meters. This is becoming more practical for
an effective defensive range.
16", the most common
barrel length sold in AR-15 carbines and the shortest length available
for general sale, gives us a muzzle velocity of of 3125. Fragmentation
range extends out to just over 100 meters, not much longer than the
The second most common barrel length for
AR-15 rifles is 20". The M193 round gets 3250 fps and a range of right
around 150 meters. This gives us a 50% increase in effective range over
the 16" barrel.
24" gives us 3300 fps, barely any
more velocity than than the 20" barrel. We've passed the sweet spot for
this particular cartridge, where additional barrel length gives us
lower velocity increases. 16 to 20 inches is really the ideal barrel
length for this cartridge. A 24" barrel gives us very little
fragmentation distance over a 20" barrel.
All of these
calculations were done around the military spec M193 5.56 NATO
cartridge. If instead you use .223 Winchester ammo offered by
Winchester, Remington, PMC or other companies, your velocity could be
100 fps lower than M193, as .223 is loaded to a lower pressure than 5.56
NATO. If you are using Wolf, Brown Bear or Silver Bear .223 ammo, your
velocities could be 150 fps slower. That can reduce effective
fragmentation ranges effectively. Using steel cased Wolf .223 ammo in a
11.5" short barrel rifle gives almost no fragmentation capability.
no means is this an attempt to talk people out of using 55gr ball
ammunition for defense. It is an ideal cartridge for defensive work,
especially in residential areas where light obstacles (like interior
walls) will cause it to fragment very quickly and reduce the chance of
missed shots striking or hurting unintended targets. But if it is the
ammo you chose to use, you should understand it's capability. Once you
extend past it's fragmentation range, you are likely better off using
another ammunition type. For instance, the 55gr TSX bullet made by
Barnes should offer reliable expansion down to 1,800 fps. This extends
the range quite a bit at which it offers good terminal ballistics. A
reasonable person could practice with 55gr FMJ ammo and use the TSX
bullet for hunting or defense to extend your effective range.
there are scores of options for 5.56 and .223 ammunition, with many
bullet types designed for different purposes. Some bullets are designed
for varmints and offer very fast expansion, some for medium game and
expand and retain weight and offer deep penetration. Choose your
ammunition wisely for your purpose.
If you'd like to see ballistic gelatin testing of various .223 and 5.56 rounds, you can review them in this pdf from ATK.