Is there an advantage to having a longer barrel on your AR-15 style carbine? For this article, we set up some simple tests to compare barrel length and performance. We fired uppers of similar design and barrel profiles in several different lengths. The law enforcement carbine has earned its place in the Big Sky rack. Deployed correctly, it is the tool that overlaps handgun and long gun use. If deployed correctly, it is the perfect tool. If deployed casually, it is like the tool that does everything, but doesn’t excel in anything.
There is a great amount of overlap in the handgun range and carbine deployment. For example, while the handgun is great as a close-quarters tool, most officers can deliver accurate fire more rapidly with a carbine at only slightly longer ranges. The carbine limits the officers’ utility in some respects, like during handcuffing, but training and equipping in force transition overcomes many of these issues. Compared to handguns, carbines can limit critical maneuverability. The trade-off of accurate effective fire and maneuverability has been subject to a little experimentation lately. That is, if we knock off just a few inches of barrel, will the carbine still be effective?
Let’s look at the first question
A carbine shortened by just a few inches, from 22 inches to about 16 inches, can dramatically improve maneuverability. When searching, a long gun’s muzzle closer to the shoulder is easier to “feel” when slicing corners. The officer can carry the muzzle at a shallower angle, which translates to quicker orientation to the target.
I grew up shooting AR-15 style carbines by placing my support hand at the magwell. Lately, I have found that slicing is more precise with the hand-forward grip because one can feel muzzle placement better. The shorter the barrel, the better the feel. I need to practice that. With the carbine on a sling at a good balance point, it can mean the difference between being able to run and climb obstacles as opposed to banging on the knees—or worse. When suppressed, the balance of the firearm can be that much closer to the shoulder, quickening the ability to address multiple targets.
Simply going from vehicle rack to a high risk traffic stop is improved with a shorter barrel in the patrol car. This shorter barrel may be the deciding factor when adding carbines to a motor unit. Carbines on motors have become increasingly more common and, frankly, should be standard issue.
Finally, if I needed to board a public transportation vehicle, the best tool is the short barreled carbine. Although these tests are not conclusive; several studies suggest the short barreled carbine or SBR may be a safer tool, as well.
What’s the down side of shorter barrels?
First, since some cartridges are engineered to continue to burn propellant up until the bullet’s exit, a shorter barrel may affect the full potential of the cartridge. Because carbines rely on the bleed of the gases to cycle the bolt, it is theorized that a shorter action using longer action components will make them less reliable. Piston advocates will say, “Use a piston; problem solved.” Actually, there is little evidence that a well-built short barrel is less reliable—just stick to the name brands.
For this test, I used Franklin Armory uppers. I’ve been shooting a Franklin Armory carbine for several years. It is one of their 7075-T6 billet lowers in black Hard Coat III. Their Libertas SBR, a similar model, comes with an Ergo Ambi Sure Grip, but mine has an Ergo Tactical Deluxe Grip with Palm Shelf and F93 Pro Stock. Franklin Armory is a manufacturer based in Morgan Hill, Calif. Although they can field large departmental orders, each is made by hand using components made in the USA. Franklin Armory has a growing law enforcement market, and they can tailor their product to the needs of a specific requirement or task.
I used complete Franklin Armory uppers in 7.5 inches, 11 inches, 14 inches and 16 inches. They use a salt bath nitride finish in their steel, including the chambers. Their aluminum parts are Hard Coat Type III and most uppers are free floated and vented. First I chronographed them, then I shot them in ballistic gelatin.
Let’s address what sells long barreled carbines: Accuracy
Most shooters consider a longer barrel to be more accurate, because of the higher velocities and more time the barrel can impart its effect on the bullet.
In fact, some studies have demonstrated that a shorter barrel can give the greatest accuracy. As a bullet travels down the barrel, the barrel stretches to accommodate it, akin to a snake swallowing a fine meal. If the barrel is against a stiff object like a fixed stock, the barrel will whip in the opposite direction, then recover, affecting accuracy. Bear in mind that accuracy in a barrel is just a matter of doing the same thing consistently. That is, if the whipping action always puts the bullet in the same place, no one would care what the barrel did. Manufacturers accommodate for this whipping action by “free floating” the barrel, not allowing the barrel to touch any hardware. Most AR-15 uppers are done this way. A shorter barrel will often have less whipping action.
Now that we’ve discussed all this, let me clarify something about carbine accuracy: Accuracy in a carbine is important, but not critical. Consider this: What is the likelihood of deploying a law enforcement carbine for a shot that exceeds 75 yards? The length of a barrel won’t affect accuracy at carbine ranges.
Whatever a law enforcement officer does with a carbine will never require match accuracy. In fact, if match accuracy is required, the officer is using the wrong tool. Instead of using a carbine, the correct tool is a rifle.
Next, consider velocity
The difference between our shortest barrel and our longest barrel was quite a big spread:
- Barrel / Average Velocity
- 7.5 inches 2,630 fps
- 11 inches 3,278 fps
- 14 inches 3,296 fps
- 16 inches 3,450 fps
As we predicted, a longer barrel seems to send a faster bullet, all other things being equal. Actually, the 16-inch barrel numbers were a little fast for a 55 grain JHP projectile, even for a muzzle velocity. I ran this one a few times, just to make sure I was reading my Oehler Model 35P correctly.
The interesting thing is how the bullets behaved in gelatin
Once again, we used Clear Ballistics Gelatin. This saved a lot of time in mixing and maintaining calibration.
The projectiles fired from the 16-inch barrel fragmented after about 5 inches of penetration. The wound channel continued for 9.5 inches, but much of the jacket was at 6.5 inches.
The projectiles fired from the 14-inch barrel shot all the way through a 16-inch long block several times, shedding some jacket at 11 inches.
The projectiles fired from the 11-inch barrel stayed mostly intact, with 85 percent of the projectile stopping at an average of 11.75 inches in a predictable, peeled back mushroom.
The projectiles fired from the 7.5-inch barrel carved an unusual, but predictable arc in the blocks, stopping at 12 inches. This delivered the highest retained weight at the bullet’s point of rest, shedding very little jacket.
All right. The first thing these tests suggest is that there may be a “sweet spot” for AR-15 cartridges, which will vary with each application. If I had to guess, it’s somewhere between 3,200 and 3,300 fps at this bullet weight, which was 52 grains. They might do best with a barrel length around 11 inches. These tests should be duplicated by the agency, using the agency’s own carbines.
The second thing these tests suggest is something I have been saying all along. Sometimes, the AR-15 is the safest law enforcement tool—if the combination has similar performance. That is, they don’t over penetrate, striking something that was not the intended target.
I cannot conclude that a shorter barrel is better. I can conclude that there is a barrel length/cartridge combination and the tools to finding them are available to any agency.
Here is a prediction: Ammunition manufacturers will likely be looking at short barrel specific cartridges using powders with faster burn rates and short range performance.
