5.56/.223 ballistic test carbine vs SBR
I have been working on a a few projects for Barnes Precision Machine, one of which was a ballistic test for a common barrel length for SBR and compare that to the AR-15 carbine 16″ barrel. Some history of the 5.56 to begin with.
The 5.56x45mm NATO began life in 1957 as an experimental cartridge based on the .222 Remington. The .222 Remington would not meet the velocity requirements so the case capacity was increased and the cartridge became the .222 Remington Special. At the time there were several centerfire cartridges designated at .222 so the .222 Remington Special was renamed the .223 and was designated the 5.56x45mm NATO in 1963. That is also when the new AR-15 rifle became the M-16 and adopted by The United States military. In 1964 the .223 Remington was introduced as a commercial sporting cartridge. the actual bullet diameter is 0.224″
With that said, the .223 Remington and 5.56x45mm are not interchangeable. While the cases are the same externally, mil spec brass may have thicker walls decreasing internal volume. The pressure and chamber specifications are not the same. The 5.56 is generally loaded to higher pressures and the mil-spec chamber has a longer leade which is the distance between the case mouth and where the rifling begins. The .223 Remington chamber however is governed by SAAMI chamber and has a shorter leade. Another chamber is the .223 Wylde, a chamber with the external dimensions and lead angle as found in the military 5.56x45mm NATO cartridge and the 0.2240 inch freebore diameter as found in the civilian SAAMI .223 Remington cartridge. So, in short the .223 Remington is held to SAAMI specs while the 5.56x45mm is not. With that in mind it is safe to fire .223 Remington in a 5.56×45 NATO chamber but firing the 5.56 in a .223 chamber could result in a pressure spike and an over pressure event.
Also, The SAAMI spec for .223 Remington is 1:12-inch twist, and many rifles will use that rate. 1:12 will stabilize bullets up to about 60 grains. With that said, many long 60-grain bullets will not. In the .223 the 1:8 and 1:9 twist rate is a great compromise. Firearms chambered for 5.56×45 mm often have a rifling twist rate of 1:7 or 1:8 inches to stabilize the longer heavy bullets. The 1:7-inch twist rate will work best with bullets heavier than 60 grains but it is generally accepted it is better to over stabilize then under, if there really is such a thing as over stabilization.
So, the goal with this ballistic test is too compare the 16″ carbine length barrel AR-15 to an 11.5″ and 7.5″ SBR as far as velocity loss and terminal performance differences. All rifles used were 1:7 twist. I used new ballistic gel with a few rounds of each sample shot over the chronograph and into bare gel, then covering the gel with three layers of blue jean denim. Switching the gel around or remelting as needed to keep the data accurate. One thing I noticed, that sometimes, the exact same round shot from the exact same rifle performed a little different. In instances such as that I would shoot a series and take the most consistent results but understand that even with all variables the same there can be differences in ballistic performance in a controlled environment, take any of the control out and results will vary more. With that said, this ballistic test will give the reader a solid baseline on how different 5.56×45 and .223 Remington ammunition preforms out of different barrel lengths.
You can reference the above charts, the rounds that are included in one chart. I will continually update the list as I can get the gel reformed. This test was over 3 occasions and the 5.56/.223 is very hard on ballistic gel.
Bullets shot from the 16″ barrel are on left and the 11.5″ on right as recovered shot through the 3 layers. From top to bottom, Hornady 75gr TAP, SBR, Hornady 55gr FMJ, Hornady 55gr V-Max, Winchester 55gr Frangable, Stillwood 68gr BTHP, M-855, Hornady 75gr NATO
Bullets shot through the 7.5″ barrel, from left to right. Hornady 55gr FMJ, Hornady 55gr V-Max, Winchester 55gr Frangable, Stillwood 68gr BTHP, Hornady 75gr NATO, M-855, Gorilla 77gr.
The Hornady 55gr FMJ provided the most prominent wound channel from all 3 barrel lengths tumbling in the gel and several times was recovered with the base facing forward. The Hornady V-Max as well as the Stillwood 68gr HPBT were the most explosive. The Hornady TAP SBR preformed very well in the 16 and 11.5″ barrel while penetrating all the way through all layers and gel, exiting the rear, leaving me to believe it expanded very little, if at all. The Winchester Frangable behaved spiratic sometimes tumbling and on a few occasions breaking in half. The Gorilla 77gr did very well out of the 16″ and 7.5″ barrel lengths but was not tested in the 11.5″
The 5.56/.223 is a devastating round primarily due to velocity, and though velocity loss became evident especially in the 7.5″ barrel but many of the rounds still offered excellent performance. The lighter bullets did very well out of the shorter barrels, and that stands to reason as they can get up to speed quicker than a heavier bullet from the same length barrel. The ballistic tipped Hornady V-Max did very well as did the plain old 55gr FMJ. For barrels about 11″ the Hornady TAP SBR expanded nicely. Also keep in mind though giving up a little with the 7.5″ barrel you add a lot of maneuverability, you just have to be a bit more selective on your ammunition. As with all firearms, everything is a trade off.
Rick Cirac, without his help this article would of been much harder and took much longer to complete.