May 08, 2017
By David Fortier
With the growing interest in Short Barrel Rifles and Personal Defense Weapons, there's an equal growing demand for hard information on their performance. Sure, short-barrel carbines handle well, carry easily and stow in tight spaces, but are their trade-offs worth it? Plus, just how short can you go while maintaining adequate terminal performance? Will your caliber of choice perform adequately from an 11.5-,10.5- or even a 7.5-inch barrel?
These are the questions Hornady addressed when it developed a 5.56 NATO load specifically for use in short barrels. Called the 5.56 InterLock HD SBR, this 75-grain load is part of the company's recently introduced Black line.
Standard ammunition fired from very short barrels produces excessive muzzle flash, blast and report. These can distract, disorient and even impair the shooter — particularly inside a room or vehicle in low/no light in a self-defense scenario with no hearing protection. The muzzle flash off short barrels typically large and bright even in full daylight.
The blast from shooting prone in dirt/sand/gravel can cause issues, especially if you're using a muzzle brake. Typically, the report is also noticeably louder than with a 16- or 20-inch gun.
Performance can be problematic as well. In a defensive situation, you need a load that can deliver adequate penetration and expansion at the much reduced velocity. Further, depending on your defensive requirements the ammo needs to be able to handle barriers like as windshields or walls.
Hornady designers incorporated a number of features to make this ammo the best it could be. For starters, they crimped the primer in place and sealed the annulus for reliable function. Next they tested a variety of powders and charge weights to reduce flash, blast and report while providing the desired exterior ballistics.
Perhaps the most important element of this load though was the development of an entirely new projectile, one that would meet the FBI protocols for penetration: a bullet that would reliably expand and provide a minimum of 12 inches of penetration, even after encountering an intermediate barrier.
The end result of this work is the InterLock HD, a 75-grain softpoint flat-base bullet with an exposed lead tip. The HD stands for heavy duty, and the the InterLock band that binds the jacket to the lead core is deeper than in the regular InterLock. It's the same approach the company uses in its Critical Duty bullet — although the latter is a hollowpoint with a polymer insert.
The InterLock HD is designed to provide controlled expansion as well as high weight retention. Hornady claims a G1 ballistic coefficient of .230 and a sectional density of .214.
The engineering team at Hornady optimized this load for use in 10.5- and 11.5-inch Short Barrel Rifles. Hornady claims this load averages approximately 2,320 fps when fired from an 11.5-inch barrel and 2,200 fps when fired from a 10.5-inch barrel. While these velocities sound a bit ho-hum, the ammo is designed to eliminate flash and dramatically reduce the sound signature. It also claims this load will not foul or overheat suppressors.
I got my hands on a small amount before its official release and decided to compare it with two Hornady loads available to the military and law enforcement: .223 Rem. 60-grain TAP Urban and 5.56 75-grain TAP T2. Comparisons were made with a "worst case" AR barrel length of just 7.5 inches and one with a 16-inch barrel.
Both my 16- and 7.5-inch ARs ran flawlessly with the 75-grain InterLock HD SBR Black load. Rounds chambered smoothly, extracted and ejected without issue to three o'clock. Report and blast were noticeably reduced when compared to the 60-grain TAP Urban load, especially on the 7.5-inch gun. It was much more pleasant to fire. Flash seemed to be all but eliminated.
Velocity was also consistent round to round. I noted a 64.9 fps loss per inch of barrel going from 16 inches down to 7.5 inches. All my shooting was done on steel at 100 yards with red dot sights, and accuracy was in the two-inch range. Practical accuracy seemed more than acceptable for this load's intended SBR purpose.
The bullet's terminal performance looks good as well. All too often .223 Rem and 5.56 expanding loads have relatively shallow penetration. Some are surprisingly shallow. As an example, Hornady's 75-grain TAP T2 load in testing conducted by Hornady's ballistic laboratory penetrated to an average depth of 10.5 inches in bare 10 percent ordnance gel; 10 inches when the gel was behind FBI protocol steel and wall board barriers; and just seven to 7.5 inches when behind auto glass and plywood barriers.
The .223 Rem. 60-grain TAP Urban load penetrates even less through FBI protocol barriers and averages between 5.5 and 9.75 inches. Testing of both of these loads was conducted using a 16-inch barrel.
Hornady's new 5.56 75-grain InterLock HD SBR Black load penetrates very well while reliably expanding. Hornady's testing using an 11.5 inch barrel showed it to penetrate to an average depth of 17 inches in bare 10 percent ordnance gel; 14.7 inches when the gel was protected by FBI protocol steel barrier; 17.2 inches after penetrating a wall board barrier; 16.7 inches through a plywood barrier; and 15.2 inches through an auto glass barrier. In bare gel it expanded to .46 inch and had a retained weight of 69.5 grains, or 93 percent.
Hornady's SBR load stayed within the FBI recommended parameters of 12 to 18 inches of penetration through all the barriers, which is impressive. I think Hornady's engineers struck a nice balance of acceptable exterior ballistics and great terminal performance. Not only that but they did it while reducing the blast and sound signature and all but eliminating the flash. And this load is very suppressor friendly.
If short barrels are your thing, you'll want to look into Hornady's new 75-grain InterLock HD SBR Black load.