CONCEALMENT 11 SBR Ammo Buyer’s Guide Rob Curtis 8 Comments, Join the Conversation Think M193 and M855 are Good Options for a Stubby Tube? Think Again. While the old 55- and 62-grain standbys work adequately in longer barrels, if you own an SBR or AR pistol, you might find yourself undergunned if you use them in a self-defense scenario. It’s not that they don’t function in shorties, or are inaccurate — quite the opposite. It’s because their full metal jacket projectiles are dependent on fragmentation for increased wounding capabilities, and fragmentation is, for the most part, dependent on velocity. The 5.56mm cartridge’s velocity is severely affected by reduced barrel length, so much so that when fired from a 10.3-inch barreled MK18, some versions of the NATO load won’t even reliably fragment at the muzzle. Now, this is not to say that SBRs are useless. Far from it. Hit someone with a 5.56 of any description and they’re not going to have a good day, even if the bullet fails to deform in any way. If we were to ask for volunteers to have a 5.5mm steel rod shoved through their fleshy bits, I’m guessing there wouldn’t be that many takers. But if we want the odds stacked in our favor, then being armed with a bullet that does something other than just bore a hole in an adversary is a good thing. After considerable research, we assembled some of the top-performing (and readily available) ammunition currently available for short-barreled carbines and put them through the wringer. Here’s what we found. Testing Protocol Our test mule is a classic SBR; it’s a Daniel Defense MK18 upper, which sports a chrome-lined, cold hammer forged 10.3-inch barrel. While chrome lining and cold hammer forging creates an extremely durable barrel, let’s just say that process isn’t the choice of those seeking extreme accuracy. So, we did our best to balance out the barrel’s tendency to produce flyers by using a Geissele SD-E trigger. That being said, we were pretty surprised with all of the groups the MK18 put out. For an optic, we installed Revic’s PMR 428 4.5-28x we had sitting on the bench, and stability for groups was provided by a typical bipod and sandbag setup. Velocity data was gathered by firing a 10-round string next to a big, orange LabRadar. Accuracy testing is reported as the best of five five-round groups shot at 100 yards on a sunny, 80-degree day with a slight breeze. Finally, each load was shot into 20-inch blocks of unadulterated, ballistically calibrated Clear Ballistics gelatin substitute at 100 yards. And that’s when sh*t got weird. Clear Ballistics Is Not Gel Despite what the Internet says, Clear Ballistics is not the same as 10-percent ordnance gel, which is what the FBI uses to test bullets. The stuff is amazingly clear, and even more importantly, it’s 99-percent less hassle than the real stuff … which is made by boiling pig bones, cartilage, and skin for hours, then drying the resulting goo. To use, mix with gallons of water and refrigerate for 36 hours to set up into a gel that, if left in the sun for a while begins to putrefy back to its natural, nasty state. Silicon Good/Silicon Bad Clear Ballistics is inorganic, (we think) silicon-based goo that’s stable up to 280 degrees F and makes for gorgeous photos of a bullet’s terminal performance. But — unlike ordnance gel, and live tissue — it contains no water and therefore produces some odd results when compared to real ordnance gel. Bullets tend to rebound inside the medium, for one, and as we found out, bullets designed to expand in water-laden tissue don’t expand as they are designed to in Clear Ballistics… and sometimes not at all. When things go well, CB is adequate for apples-to-apples comparison of terminal performance, but the results aren’t analogous to those offered by ordnance gelatin. When they go wrong, bullets don’t expand and rounds go through the stuff like Rosie O’Donnell goes through cheesecake. So, when looking at our results, know that penetration and bullet expansion numbers don’t equate to those gathered from tests using 10-percent ordnance gelatin, but they do present accurate, if anecdotal, data across the confined sample set we produced in this article. The Mechanics of Wounding There’s a lot of bullsh*t spewed about how bullets inflict damage in soft tissue. Here’s a quick test to use should you encounter a self-proclaimed expert in the subject and wish to gauge their bona fides. If anyone uses the terms “energy transfer,” “knockdown power,” or “hydrostatic shock” they probably got their facts from a gun show blowhard, the internet, or a gun show blowhard on the internet. There are two mechanisms by which bullets inflict trauma on tissue other than bone. The first and most important is through crushing. The more tissue a bullet crushes, the more damage it causes and this is dependent on the surface area it presents as it moves through flesh, as well as the depth to which it penetrates. Bullets can present more surface area by mushrooming, or fragmenting, or by yawing so that they travel more or less sideways through the target. The second way damage is caused, is by means of the temporary stretch cavity bullets produce in soft tissue, as they shove it away from their path. As this tissue is pushed outward, it’s stretched and vulnerable to additional damage from bullet fragments (or bone, should one be hit) — think of a balloon; if it’s inflated, a pin prick causes it to burst and tear, while if there’s no air in it, the same tiny hole causes, well, a hole. From left to right: Black Hills 77gr Tipped Match King; Barnes 62gr TSX VOR-TX; Federal 62gr Fusion MSR; Hornady 75gr InterLock HD SBR; Nosler 64gr Defense Bonded Solid Base. Barnes Bullets 62gr TSX VOR-TX MSRP: $24/20 URL: www.barnesbullets.com Test Results Average Velocity (FPS): 2,694 Velocity Standard Deviation: 15.3 Velocity Extreme Spread: 43 Average 5-Shot Group: 1.2 MOA Best 5-Shot Group: 0.92 Wound Track Length: 28 inches Cavity Initiation: Begins at 1 inch Cavity Length: 5 inches Bullet Expansion: 189% Bullet Weight Retention: 100% Note: There are two wound tracks above. They appear to overlap, but are several inches apart. The near shot is the one we used for this evaluation. The further, with the later cavitation, was our first attempt and the bullet didn’t have enough moisture in the tip to expand properly. NOTES Barnes Bullets is the pioneer of the monolithic copper bullet. We were curious to see how this well-regarded hunting round stacks up against more recent designs. The annular rings or relief bands cut at the base give displaced copper someplace to collect, reducing fouling considerably and aid in bullet obturation, increasing accuracy. We noticed neck tension was fairly light, but not light enough to make us worry about setback issues with loaded cartridges. VOR-TX ammo delivers considerable accuracy. We collected a 1.2 MOA group that’ll hand out better than minute-of-beer-gut hits out to several hundred yards without breaking a sweat. With a muzzle velocity standard deviation of 15.3, while not quite at a match ammo level of accuracy, we found charge weights varied by a tenth of a grain across a 10-round sampling. That’s good for factory ammo. All in all, unless you’re sniping bad guys from 900 yards, we can’t see accuracy holding anyone back from using this load in your home/self defense SBR. We had to shoot the Barnes a couple times to get the bullet to do its thing in the CB medium. After the bullet failed to expand on the first shot, we scratched our head — after all, we’ve had devastating real-world success with them in the past. Then, we consulted our friend Richard Mann who suggested introducing a bit of water to the tip. The CB medium, he surmised, is too thick to squeeze through the bullet’s small tip orifice and start expansion. Since living tissue is mostly water, it makes sense that bullets designed to expand in a moist medium will struggle with this stuff. We layered up a few wet paper towels on the front of the Clear Ballistics block and that did the trick. Side note, if you ever hear reports of a 5.56mm TSX round failing to drop a homicidal, top-heavy woman, ask if she had silicone implants. The long, light, and fast projectile hits with 793 foot-pounds of energy thanks to its 2,694 fps muzzle velocity, which is about 200 fps faster than the other rounds we tested. That’s a big hammer and the projectile managed to maintain 100 percent of its mass while expanding to almost twice its diameter. The 28-inch penetration in fake gel seems like a lot, but all we can say is that we’re using fake gel. Black Hills Ammunition 77gr Tipped Sierra Match King MSRP: $60 URL: www.black-hills.com Test Results Average Velocity (FPS): 2,398 Velocity Standard Deviation: 15 Velocity Extreme Spread: 40 Average 5-Shot Group: 1.28 MOA Best 5-Shot Group: 0.52 Wound Track Length: 28 inches Cavity Initiation: At 1.5 inches Cavity Length: 6.5 inches Bullet Expansion: 200% Bullet Weight Retention: 63.1% NOTES The original Black Hills 77gr SMK was developed more than a decade ago in response to the U.S. Army and U.S. Navy’s need to feed the 18-inch 5.56 MK12 Designated Marksman Rifle. The resulting round, known as Mk262 Mod 1, became renowned for both its accuracy and terminal ballistic performance during the war in Iraq and Afghanistan. The cartridge we’re looking at is an updated version with an improved BC and a ballistic tip to increase ballistic coefficient. The 77gr tipped SMK is a thin-jacketed, unbonded match round. It’s unlike many of its competitors in the tactical realm that tout their bonded construction and weight retention for better barrier ballistics. This bullet’s key feature is its ability to do the opposite, to fragment. When this bullet clubs someone up close, it fragments fast and dumps an absolute assload of frags into the wound. This load hauls an estimated 811 foot-pounds of energy at 100 yards, carrying the most energy to the target in our ammo test group. The resulting wound track and cavity are brief, but eventful. The bullet upended, headed downward, and at some point, the lead core split from the thin copper jacket and continued on for an inch or so, coming to rest after producing a 12.9-inch wound track, hitting the mark for the FBI’s minimum penetration performance. Compared to the other bullets in the group, this is the shortest wound track and the short track indicates the bullet used its energy in an explosive manner, consistent with the separated core and jacket. The wound cavity is about 6.5 inches, and shows what we’d expect from such a healthy blast into gel, a 2- to 3-inch-wide permanent cavity. Federal Ammunition 62gr Fusion MSR MSRP: $22 URL: www.federalpremium.com Test Results Average Velocity (FPS): 2,500 Velocity Standard Deviation: 29.9 Velocity Extreme Spread: 95 Average 5-Shot Group: 1.63 MOA Best 5-Shot Group: 0.63 Wound Track Length: 20.25 inches Cavity Initiation: At 1 inch Cavity Length: 7 inches Bullet Expansion: 249% Bullet Weight Retention: 86% NOTES Federal’s MSR cartridges are about five years old and were made to address the growth of hunters running semi-auto AR platforms. The lacquered primer in the MSR line is a little tougher than what you might find in other hunting cartridges to mitigate slam fires that can happen with the AR’s free-floating firing pin. The brass has that dirty look from post-wash annealing that the military requires as an indicator that the cases are properly annealed after neck sizing. Federal uses this marking to differentiate the MSR line from its other hunting rounds. The company also used custom propellants with flash suppressing chemistry and optimized charge weight for a 16-inch barrel, vice a 20-inch-plus barrel normally found on a bolt-action hunting rifle. Shorter barrels call for faster burning propellant that’ll get the bullet up to speed without spewing flame and unburned powder while providing enough gas to cycle a semi-auto action. The bullet itself is made using Federal’s Fusion process, which uses electrolysis to molecularly bond a lead slug with the copper jacket before the bullet is formed. That’s the opposite of traditional cup and core construction in which a lead slug is dropped into a copper jacket, forming a mechanical bond between the two materials. Federal says its Fusion process results in higher weight retention, which leads to more controlled expansion, and with 86-percent weight retention and 249-percent expansion in our gelatin test we’re obliged to agree. Retaining more than 80 percent in a non-bonded or non-monolithic bullet construction is solid work. The bullet began to cavitate within an inch of entering the gel and proceeded to belch out a ripper for another 7 inches before it augered to the end of our 20-inch block, stalling just past the threshold into the abutting block. Based on the 2-inch width of the permanent wound cavity and its 7-inch length, the round gave up most of its 690 foot-pounds quickly and the hot round melted the goo in front of it as it drifted gently to a stop in the suspension. Hornady 75gr InterLock HD SBR MSRP: $20/20 URL: www.hornady.com Test Results Average Velocity (FPS): 2,269 Velocity Standard Deviation: 15.7 Velocity Extreme Spread: 45 Average 5-Shot Group: 1.43 MOA Best 5-Shot Group: 1.05 Wound Track Length: 40+ inches Cavity Initiation: None visible Cavity Length: None Visible Bullet Expansion: Unrecovered Bullet Weight Retention: Unrecovered NOTES This is the weird one. We can’t say for sure why the exposed lead tip of Hornady’s 75gr InterLock SBR bullet didn’t mushroom out when it came in contact with the Clear Ballistics media. Lord knows we tried. We shot cartridges from three boxes into a couple of blocks, even switching them around for the hell of it. No matter what we did, those InterLock projos zipped straight through 40 inches of material without fail. The 75gr InterLock bullet was designed in 2015 in response to the FBI’s request to industry for a short-barreled rifle-specific cartridge. The FBI was looking for a round with a more efficient, cleaner powder that could run in a 10.5- to 11.5-inch semi-auto carbine. It needed a bullet that could expand at the reduced velocities SBRs put out, too. The FBI’s test protocol gauged bullet performance by shooting bare gelatin, heavy clothing, auto glass, 3/4-inch plywood, two sheets of drywall, 20-gauge sheet steel, and a 100-yard bare gel test. Since the InterLock passed the FBI test protocol, we assume it’d open up when hitting our gel block. And yet, it did not. In our quest to recover one damned bullet, we fired 10 rounds through the blocks and while a handful of them showed some cavitation, we had to wonder if that was just the unexpanded bullet yawing and creating turbulence through the gel. The majority of the bullets tracked straight through, but a few yawed and exited the block’s sides and top. We spoke with Hornady ballistician Jayden Quinlan about the bullet’s performance. He was surprised the bullet didn’t open since it was designed to expand in gel when moving as slow as 1,900 fps. He said Hornady can’t guarantee any results when using synthetic gelatin because they don’t use it in their own testing. While we can’t talk much about its terminal performance, we can say that it produced respectable groups for a round made for close-quarters battle and its velocity was equally as consistent with an SD of 15.7. We’ve no doubt we could hit whatever we aim at, but until we mix up our own ordnance gel for a retest, we’ll assume the Clear Ballistics was the problem, and not the bullet. Nosler 64gr Defense Bonded Solid Base MSRP: $21/20 URL: www.nosler.com Test Results Average Velocity (FPS): 2,432 Velocity Standard Deviation: 46.9 Velocity Extreme Spread: 129 Average 5-Shot Group: 0.79 MOA Best 5-Shot Group: 0.52 Wound Track Length: 24 inches Cavity Initiation: At 0 inches Cavity Length: 9 inches Bullet Expansion: 181% Bullet Weight Retention: 100% Note: Ignore the lower wound track. NOTES At about five years old, Nosler’s Bonded Solid Base Defense ammo design is relatively new. Like its competitors, the company wanted to add a bullet to its catalog designed for MSRs, with a tip that can take getting smacked around inside a mag and on its way into the chamber. The bullet was designed around four requirements; reliable feeding, high weight retention, reliable expansion, and maximum penetration. Based on our accuracy, ballistic and forensic evaluation, Nosler nailed all four of those attributes. We had no malfunctions with the round, recorded 100-percent weight retention, 181-percent expansion, and 24 inches of travel through Clear Ballistics gelatin. Accuracy-wise, holy crap. We had to check after the first five-round group that we hadn’t accidentally loaded a match round. We didn’t know our MK18 could print a 0.79 MOA group, let alone a 0.52. We thank whoever made that blood sacrifice to the MOA gods on our behalf. We pulled a couple handfuls of cartridges apart to measure the case-to-case powder variation and were not shocked to find it varied by 1/10 of a grain. The overall cartridge length only varied by 5 thousandths. Those numbers are pretty much within the realm of handloading. The bullet tracked straight, with a little porpoising after expansion. It hit the block with 609 foot-pounds of energy and the bonded bullet maintained all its weight. 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