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SBR ballistics: just how much are you giving up when you bob that barrel? Internet commandos exaggerate the effect, Tarr says: an SBR can be plenty effective with the right ammo.

For my recent roundup of AR pistol braces in these pages (Issue 16), I put together an AR pistol, and I will be detailing that build in an upcoming article. My new pistol sports an 11.5-inch barrel, and as I contemplated it shortly after putting the pistol together I wondered what kind of performance I could expect from bullets out of the shorter-than-rifle length barrel.

So I went on the internet to do a little research. Oh boy.

Reading the wisdom of the "experts" lurking in the online forums, I learned that short-barreled AR rifles/pistols are pretty much useless for any serious work, because they don't provide enough velocity to guarantee tumbling and fragmentation in M855/SS109 and M193 projectiles.

My immediate thought was, unless you're active duty military, why the heck would you be using military ball ammo for self-defense? It's just dumb. But the internet is perhaps the purest democracy to ever exist on the planet, where everyone has equal access, no matter how uninformed or just plain stupid he might be.

The marketplace is filled with modern defensive .223/5.56 projectiles designed to expand or fragment or otherwise take care of business after impacting the target, but I couldn't locate much data on their performance out of barrels shorter than 16 inches.

So, I reached out to Jeff Hoffman, President of Black Hills Ammunition, to see if they'd done any ballistic gel testing using short-barreled rifles (www.black-hills.c0m).

The results filled my inbox for days, and I think you'll find them as interesting as I do.

First, for those of you unfamiliar with Black Hills Ammunition, in addition to producing commercial ammunition, they have a lot of military contracts and produce most, if not all, of the specialty ammunition used by U.S. Special Forces. Let that sink in for a moment.

And they have a world-class ballistics laboratory on site, which I have visited. All test data and gel block photos in this article come directly from Black Hills. All sarcastic comments and obnoxious opinions are from yours truly.

Just a reminder, 10% ballistic gelatin is a tissue simulant designed not just to mimic the general density of a person but be a repeatable test medium.

Performance in gel should be a good indicator of how that bullet will do against a person, but no test medium is perfect. Gel blocks are completely homogenous and don't have muscle or bone. In the photos, red dye has been injected into the bullet track/temporary cavity to make them more visible.

And a final note--this article is technically about bullet performance at lower velocities, not necessarily out of short barrels. Shorter barrels equal less velocity, so the performance you get out of, say, a 10-inch barrel at pointblank range might be what you get out of a 16-inch gun at several hundred yards. Keep that in mind.

Most of the ammunition tested was manufactured by Black Hills, but Black Hills loads their ammunition with cherry-picked bullets manufactured by most of'the biggest names in the industry. Below you'll see tests of bullets made by Sierra, Barnes, and Hornady, three of the biggest names in the industry. These results are about how these specific bullets (and bullet types) perform at lower velocities. I've sorted the results by bullet type.

A final note--while I will be generally talking about one specific gel test for each of these loads, with accompanying photos of the gel blocks, don't think only one round of each type was fired. Ballistics labs, such as the one at Black Hills, test dozens of rounds of each type of ammo, this article is just covering representative examples.

Military Loads

M855/SS109

Let's start with the military projectiles. Modern military forces are generally stuck with non-expanding bullets as a result of the Hague Convention of 1899. Which means military rifle bullet types available to civilians consist of either full metal-jacketed projectiles ("ball") or light armor piercing rounds like the M855/SS109 bullet, which features a steel penetrator.

Sorry, no explosive-tipped or incendiary rounds for you, no matter how useful they'd be. The M855 5.56 round (also commonly known as the SSI09 NATO or "green tip" ammo) offers a 62-grain bullet with a steel penetrator inside a jacketed lead bullet.

If this bullet is moving fast enough, it tends to tumble upon impact, but at distance or out of barrels shorter than 14.5 inches, this bullet has a reputation for zipping right through bad guys without yawing or imparting much hydrostatic shock, which is what creates the "temporary cavity" in gel testing.

I remember reading in Black Hawk Down the complaints about the poor terminal performance of this then new round against thin Somalis--the bullets would create "icepick" wounds and pass all the way through before having a chance to tumble.

First, let's look at how this military ammo performs out of our most common military rifle, in this case a 14.5inch barreled Colt M4A1 carbine. Ammunition used was produced in the Lake City ammunition plant. Out of the Colt, it provided 2841 fps. The bullet began to yaw 1.25 inches into the block and created a temporary cavity 10.5 by 5.5 inches.

Some fragments came off the bullet and stayed in the block, but the bullet itself penetrated 147/s inches and shot out the side of the block, to be recovered on the floor. The front half or so of the bullet is what exited the block, and it weighed 29.9 grains.

To be honest, Jeff Hoffman sent me several gel tests of M855 ammunition out of 14.5-inch barrels, and every one of them was drastically different. Bullets passed all the way through the block or yawed and shot out the side or top. I picked this gel test as it was pretty average. The temporary cavity was a good size, but the bullet does not expand or reliably fragment.

For short barrel testing, Black Hills used a 10-inch barreled HK 416D and the same Lake City M855 ammunition. Out of the 10-inch barrel, this ammo provided 2576 fps, a drastic decrease from the 14.5-inch barrel, and it significantly affected performance.

The bullet traveled more than 4 inches into the gel block before it began to yaw and create a temporary wound cavity. The temporary wound cavity was a decent size, 12.5 by 5.6 inches, but the bullet plowed straight through the 17-inch-long block. It exited the rear of the block but didn't have enough force left to penetrate the second block.

The recovered bullet lost a few fragments but otherwise is whole, just a little bent. Other than the hydrostatic shock given to the block due to the bullet's velocity, this bullet didn't do much, and it is easy to see why soldiers have been unimpressed with its terminal performance.

However, I know several Iraq veterans who love this ammo specifically because how well it reached through car doors and windshields. Not everyone wants the same things out of their ammo.

Remember, gel blocks for this testing are positioned 12 feet from the muzzle, so the velocity obtained from a 10-inch gun at the muzzle is what you get from a 14.5 or 16-inch rifle at about 100 yards.

Mk262 Mod1

This is the go-to round for everybody serving in Afghanistan. It features a heavy 77-grain BTHP bullet that bucks the wind better and retains velocity much better at longer distances than 55- or 62-grain bullets.

While the bullet in this cartridge technically has a hollow tip, the bullet is not designed to expand. That cavity is a result of the manufacturing process, and so this bullet has been approved for military use.

The Mk 262 Mod 1 round was actually developed in part by Black Hills, and they currently manufacture it for the U.S. military. Because the bullet is long for caliber, it tends to yaw and break apart on impact with the target, providing better terminal performance than M855 ammunition ... at least out of longer barrels. I was curious to see how well it did out of short barrels, and the Black Hills ballistics lab sent me performance data out of a 10inch barreled rifle.

Out of the ballistics lab's 10-inch HK 416, this load provided 2421 fps. It penetrated just 1 inch before yawing and creating a temporary wound cavity 9.5 inches by 5.75 inches. The base of the bullet penetrated 23.375 inches.

Even out of a short barrel, this round performed as expected. When it began to yaw, the long 77-grain bullet broke apart at the cannelure and ultimately into four pieces--base, copper nose jacket, and two pieces of lead, all of which penetrated at least 10 inches.

While this isn't an "expanding" bullet, even at lower velocities, this military round has much better terminal performance than standard FMJ ammo, but I still wouldn't consider it suitable for hunting or even ideal for self-defense.

Tipped Bullets

If I'm not mistaken, the first polymer-tipped rifle bullet was the Ballistic Tip. Rifle bullets have narrow tips, so a traditional hollow-point would be small ... and yet still screw up the bullet's ballistic coefficient. The Nosier Ballistic Tip took a rifle bullet with a big hollow point and covered it up with a polymer point.

As a result, it had an aerodynamic profile like a FMJ bullet, but when it hit, it performed as well if not better than a standard hollow-point as that polymer nose-cone was forced back into the cavity, opening it up.

Perhaps the most well-known polymer-tipped rifle bullet these days is the Hornady V-Max. Generally these bullets have thin jackets and expand rapidly, which is why they are very popular with varmint and predator hunters. They are also popular with law enforcement agencies concerned about overpenetration, as these bullets will start to break apart when fired through very light barriers such as dry wall.

These bullets are loaded into ammunition made by a number of companies, and Black Hills tested its .223 Rem. round loaded with the 50-grain V-Max bullet. Out of an LWRC rifle with a short 8.5-inch barrel, this load provided only 2371 fps, but still the bullet performed as expected.

The bullet began to expand just .625" into the gel block and exploded into 35 pieces, if you count the polymer tip. The base of the bullet, the heaviest piece, penetrated just 8.25 inches, but the shrapnel-filled temporary cavity behind it looks like a watermelon filled with seeds. The temporary cavity was 7% by 4.25 inches in diameter.

At the other end of the tipped-bullet spectrum is the new 77-grain TMK--Tipped Match King. The bullet is from Sierra, and was initially developed working with Black Hills Ammunition. Sierra's 77-grain MatchKing bullet is world-renowned as being accurate and having great BC, but it was never designed to expand. The TMK is. Not only is the jacket a little thicker on this bullet when compared to the V-Max, it is heavier overall so the base tends to penetrate more deeply.

Out of the 10-inch barrel of Black Hills' HK416D, this load reached 2387 fps. Twenty-five pieces fragmented off of the base, three quarters of them penetrating the block at least 7 inches. The base of the bullet, weighing 46.4 grains (60.2% of the total) expanded to .505" and penetrated 12.5 inches into the block. So with this load you get fragmentation, expansion, and penetration.

The 77-grain Tipped Match King has a great ballistic coefficient, and compared to shorter, lighter, bullets it retains velocity better. As Black Hills has done a huge amount of testing of their Mk 262 Mod 1 bullet at distance, it only made sense that they would test this new 77 -grain TMK at distance as well, and they sent me gel test data on this bullet at a simulated 500 yards out of a 10-inch barrel.

For the simulated 500-yard gel test, the 77-grain TMK was travelling at just 1756 fps when it hit the block--but that's still some impressive velocity retention. The temporary cavity was small, just 8.5 inches by 33A inches, and it didn't start until 2.5 inches into the block, but the bullet still performed impressively. Sixteen small pieces of jacket and lead broke off as the front section of the bullet fragmented, but the base of the bullet weighing almost 50 grains expanded in textbook fashion and penetrated 18.75 inches.

Copper Solid Bullets

"Copper solid" is the common shorthand term for bullets that are constructed of homogenous copper alloy. Unlike traditional bullets, there is no copper jacket and lead core; rather, the entire bullet is all one piece.

Because of that monolithic construction, copper solid bullets tend to fragment less and penetrate more deeply than traditional bullets of the same weight. In boxing terms, they punch above their weight. As the copper alloy is slightly lighter than lead, these bullets also tend to be longer than traditional bullets of the same weight.

Black Hills loads Barnes Bullets' copper solid TSX bullets into a number of cartridges. Perhaps their most popular is the 5.56 NATO 50-grain TSX load. The TSX bullet has a small hollow point in the tip but is otherwise unremarkable in appearance.

I have seen a number of gel tests put on by Barnes and these bullets always perform well. The Barnes people have told me that TSX bullets need about 2000 fps (depending on weight and caliber) to begin expansion.

Out of the 10-inch barrel of Black Hills' HK416D, this load provided 2877 fps, which is pretty impressive. The high velocity resulted in a temporary cavity measuring 10 1/8 by 5 1/2 inches, that cavity starting just half an inch from the front of the block. The bullet did not fragment at all. but expanded in a textbook manner to .495". The bullet penetrated 14.75 inches.

This bullet weight seems to be the Goldilocks weight for the TSX bullet in .223/5.56. It penetrates to the same depth in gel, no matter how fast or slow it is going. Whether it is fired out of 10-inch or 20-inch barrels, the bullets expand greatly and only penetrate 14-16 inches. It's apparently too light to penetrate gel much further, and too tough to fragment, so when going faster it just expands more.

Law enforcement likes to use the term "barrier blind" when talking about homogenous bullets like these, as they still tend to perform well even after penetrating intermediate barriers such as car doors and auto glass. Black Hills markets this 50-grain 5.56 TSX load to LE agencies, as they think it offers the right balance of penetration and expansion.

In fact, they offer a version of this load with an "Optimized" 50-grain Barnes TSX bullet proprietary to Black Hills Ammo. The bullet has been slightly redesigned to optimize performance through barriers such as auto glass and sheet metal. It generally expands a bit less, and penetrates maybe an inch more, all other things being equal.

The heavy end of the copper solid spectrum is occupied by the 70-grain bullets. Because they are longer than traditional lead-core bullets, you can't load a copper solid bullet heavier than 70 grains into a .223/5.56 case--not and have it be short enough to fit into an AR15 magazine.

Black Hills' 70-grain load features the Hornady GMX bullet. This bullet has a hollow point, and the heavier weight and solid construction means that it's all about the penetration, at least when compared to lighter bullets. Black Hills offers them loaded into a 5.56 cartridge, which means slightly higher pressures and velocity than the .223 Rem.

Out of Black Hills' 10-inch barreled LMT, this load produced 2605 fps. The temporary cavity in the gel block started right as the bullet entered and measured 12.5 inches by 5.5 inches. The bullet did not fragment at all and expanded to an average diameter of .568", with its largest diameter .738"! Compared to the 50-grain TSX, which never seems to plow deeper into gel than 16 inches no matter how fast or slow it's going, the 70-grain GMX bullet penetrated 20.5 inches.

Going Old School-Soft Point Bullets

There is not a lot of real estate in the pointy nose of a rifle bullet, but one thing a rifle bullet does have going for it is velocity. Some enterprising soul discovered that if you expose the lead tip of a jacketed rifle bullet, upon impact that lead tip mushrooms and expands, while the jacket ensures both reliable feeding and the body of the bullet staying together after impact. Such bullets these days are called "soft point" bullets, and while they are the original expanding rifle bullet, they still work just fine.

Black Hills makes a .223 Rem. load tipped with a 60-grain Hornady soft-point bullet. Jeff Hoffman himself likes using this load to hunt deer--but that is out of a rifle. Whether or not a short-barrel will give the bullet enough velocity to expand and/or penetrate is the question.

Black Hills' ballistics lab used their 10-inch barreled LMT carbine to test this round. Out of that 10-inch tube, the round provided 2557 fps. The temporary cavity in the block started just half an inch in, and measured TA by 51/4 inches. The bullet shed 11 small pieces of jacket and lead in the gel but the base, weighing 35.9 grains (60% of the total) expanded to an average diameter of .419" and penetrated the block 12.5 inches.

Conclusions

The results of these gel tests honestly surprised me. Not that M855 bullets curve through gel blocks and barely break apart even out of M4-length barrels; that I expected, but that every other type of expanding bullet worked more or less as it should even out of 10-inch and shorter barrels.

The Hornady V-Max bullet still blows up in the target even when fired out of an 8.5-inch barrel. While I'd been told by company reps that copper solid bullets like the TSX and GMX would expand at anything over 2000 fps, it was nice to confirm that.

The 77-grain OTM bullet in the Mk 262 Mod 1 military load fragmented nicely even out of a 10-inch barrel. Perhaps the most surprising to me was that the new 77-grain Sierra Tipped Match King bullet expands and fragments even at 1756 fps, which is closer to magnum pistol than rifle velocities.

You may not own a short-barrel rifle or AR pistol, but if you look at the velocities obtained, they will be how fast the bullets out of your 16- or 20-inch barreled rifle will be travelling at 150-300 yards, depending on the bullet. At 100 yards, bullets fired out of .223 Rem./5.56 NATO cartridges generally will be travelling about 300400 fps slower than they were at the muzzle.

For example--Black Hills' 60-grain SP load will do 3100 fps out of a rifle-length barrel, compared to the 2557 fps it provided out of a 10-inch barrel. The Hornady bullet in that load has a .264 BC, and if you throw those numbers into a ballistics calculator you learn that out of your rifle you get the same velocity at 150 yards as you do with a 10-inch SBR at the muzzle. 150 yards is not a great distance.

I think most people are unaware just how fast rifle bullets lose velocity.

To my mind it's this simple--if the bullet out of a rifle works well for hunting out to 300 yards and beyond, it will perform just as well out of an SBR at urban distances, because the velocities will be identical.

As for those internet denizens who will look at all of the above concrete data and still adamantly state that short-barreled ARs are useless for any "serious" work, I think they can best be described by the late Gene Wilder's great quote from Blazing Saddles: "You've got to remember that these are just simple farmers. These are people of the land. The common clay of the new West. You know ... morons."

LENGTH MATTERS

When it comes to shorter-than-16-inch barrels on ARs, everyone has their preferred length. Some people have the "shorter is better, period" point of view. And I'm not going to say they're wrong, short guns are eminently maneuverable. Just be aware that the shorter the barrel, the more velocity you lose.

I've tested really short-barrel ARs. Yes, they're short and handy, but I was shocked at how little velocity you get out of a 7.5-inch AR barrel. Most 55-grain loads will do little better than 2200 fps, with a huge amount of noise and flash unless you mount a really, good flash hider on the end of the barrel. Then it's just a huge amount of noise.

To my mind, there is a happy medium between overall AR length and velocity. For me, that Goldilocks-length barrel is 11.5 inches. On direct gas impingement guns, the gas port is far enough back from the muzzle that the guns tend to be much more reliable than 10 to 10.5-inch guns. Plus, the muzzle blast isn't nearly as crazy as on 7.5-inch barrels. The Colt Commando, I believe was the first 11.5inch AR/M16 variant and it is probably the most famous, thanks in part to the bank robbery scene in the classic movie Heat.

An 11.5-inch AR is still handy enough for use indoors and out of vehicles, but you get close to 500 more fps than you would with a 7.5-inch barrel.

At first, these velocity numbers don't seem to make sense. An 11.5-inch barrel is only 4 inches (53%) longer than a 7.5-inch barrel, and .223/5.56 generally gives up 25-50 fps per inch of barrel, which means at most a 200 fps difference, not 500.

But you have to remember that the first 2.2 inches or so of that barrel length is chamber.

When comparing 7.5-inch and 11.5-inch barrels, you're comparing 5.3-inch and 9.3-inch rifling lengths, and while that still only works out to a 4-inch difference, there the 11.5-inch tube provides 75% more true barrel length. 75%!

Once you move past 11.5 inches, the increased velocity is much more incremental. Depending on the load, you can see nearly the same velocity jump ( 150fps) when going from a 10-inch barrel to an 11.5-inch as you do when moving from an 11.5-inch to a 14.5-inch barrel.

Caption: The two most popular military bullets available on the civilian market right now--the 62-grain FMJ light armor piercing bullet with steel penetrator found in M855/SS109 ammunition (I.), and the 77-grain Sierra OTM bullet found in Mk262 Mod 1 ammunition.

Caption: The 62-grain M855 out of a 14.5-inch barreled Colt M4A1 produced a decent-sized temporary cavity, but this bullet's performance in gel is unpredictable. Some fragments came off the bullet and stayed in the block, but the bullet itself penetrated 147/s inches and shot out the side.

Caption: Out of the shorter 10-inch barrel, the M855 bullet traveled more than 4 inches into the gel block before it began to yaw and create a temporary wound cavity. The temporary wound cavity was a decent size, 12.5 by 5.6 inches, but the bullet plowed straight through the 17-inch-long block.

Caption: The recovered M855 bullet fired from a 14.5-inch barrel. M855 bullets do not expand; if moving fast enough, they yaw and rip themselves apart inside the block.

Caption: Out of a 10-inch barreled HK416, the M855 bullet only achieved 2576 fps, and as a result, barely deformed when hitting the gel. This is pretty poor performance.

Caption: Because it is so long for its diameter, the 77-grain OTM bullet in the Mk 262 Mod 1 load tends to yaw and break apart. Even out of a short 10-inch barrel, the bullet produced a temporary wound cavity 9.5 inches by 5.75 inches. The base of the bullet penetrated 23.375 inches.

Caption: The recovered Mk 262 Mod 1 77-grain OTM bullet fired at 2421 fps. These do not expand per se but rather yaw and usually break in half at the cannelure, as seen here.

Caption: Polymer-tipped Hornady V-Max bullets are known for violent expansion, and even doing 2371 fps out of an 8.5-inch barrel--the bullet shredded the gel block. The temporary cavity is short and wide, and the base of the bullet penetrated 8 1/2 inches.

Caption: A more robust polymer-tipped bullet, the 77-grain Sierra Tipped Match King, was doing 2387 fps out of a 10-inch barrel when it hit the block. It fragmented, expanded nicely, and the base of the bullet penetrated more than 12 inches.

Caption: Even at velocities less than 2400 fps, the Hornady 50-grain V-Max bullet provided textbook performance in the gel block, fragmenting into 35 pieces.

Caption: At 2387 fps, the front half of the 77-grain Tipped Match King bullet fragmented, while the heavy base expanded to .505" and penetrated well into the block.

Caption: At a simulated 500 yards, the 77-grain Sierra Tipped Match King bullet still performed, even doing just 1756 fps. The temporary cavity started 2.5 inches into the block, and the base of the bullet penetrated almost 19 inches.

Caption: The 5.56 NATO 50-grain TSX load produced an almost textbook cavity in the gel block out of a 10-inch barrel. The temporary cavity begins just a half inch into the block and measures over 10 by 5.5 inches. The spiral path of the bullet can be seen, as can the picture perfect expansion of the bullet, with an expanded diameter of .495".

Caption: At 1756 fps (simulated 500 yards), the fragmentation of the 77-grain TMK bullet was reduced. The base of the bullet, weighing more than 50 grains, expanded nicely.

Caption: Copper solid bullets like these 50-grain Barnes TSX provide beautiful copper flowers .45"-. 50" in diameter, with consistent and deep penetration and good expansion.

Caption: Here's a gel test of a 70-grain copper solid Hornady GMX bullet out of a 10-inch barrel, with all of the pertinent data labeled. This bullet provided a good-sized temporary cavity, which began as soon as it entered the block, as well as penetrating deeply.

Caption: Soft-point bullets are the original expanding rifle bullets, and they still perform well, even at lower velocities. Here, travelling at 2557 fps out of a 10-inch barrel, the bullet penetrated the block 12.5 inches and expanded to an average diameter of .419".

Caption: 70-grain Hornady GMX bullets fired from 10-inch barrels. Because they are heavy for caliber and tough, these bullets penetrate deeply even though they expand well. And performance is very consistent.

Caption: Bits of the jacket and pieces of lead broke off the Hornady 60-grain softpoint bullet, but the base expanded to .419" and retained 60% of the weight.

Caption: Black Hills Ammunition .223 60 Gr. Soft Point 10" barrel

Caption: The homogenous copper alloy, otherwise known as "copper solid" bullets. The Barnes 50-grain TSX on the left, and the 70-grain Hornady GMX on the right. Both expand consistently, even at SBR velocities, but the 70-grainer penetrates more deeply.

Caption: Tipped bullets combine hollow-point performance with FMJ ballistics--the 50-grain Hornady V-Max (I.) and the newer 77-grain Sierra Tipped Match King.

Caption: Soft-point rifle bullets may be very old school, but they still work, and a lot of manufacturers still offer them for that very reason. On the left is an economical 55-grain Wolf SP, on the right is the bonded 62-grain Federal Fusion bullet favored by hunters and law enforcement.

Caption: Tarr thinks the perfect short barrel length for an AR is 11.5 inches, as epitomized by the legendary Colt Commando. Below that length, velocity falls off a lot.
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Author:Tarr, James
Publication:Firearms News
Date:Jul 1, 2017
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