Ok, gang the AR pistols are all the rage right now, they are light, handy, and really look evil, but "what about the lousy ballistics?" or "You have an expensive toy there" some decry.

To recap, the 5.56 round yaws when entering a soft body, which causes too much pressure on the cannelure causing the round to physically break apart sending fragments into the wound cavity and causing some horrible wouding action.

Many round types exist, but the base model for comparion is the Lake City 55 grain FMJ, which reliably fragments coming out of 16 inch barrels. As the barrels get shorter, the velocity decreases, and around 2500 FPS or so, any significant fragmentation stops.

This usually leads to mocking of the weapon with laughter about deep ice pick wounds.

Keep in mind, there are more choices than just 55 grain 5.56, and as the weight of the bullet increases, the fragmentation threshold decreases. I presume this is happens, because there is more mass pushing on the copper jacket, thus the fragmentation velocity threshold decreases. Then again...I got an F in physics the first go around in college, so take my physics theory with a grain of salt.

The questions "Can an AR pistol function as a reliable home/personal defense weapon? Will heavier ammo fragment from a 7.5 inch barrel?"

The premise "Heavier Bullets have a lower fragmentation threshold, so even with the lower velocity coming out of a 7.5 inch barrel, the round should still have enough kick to fragment."

Control "9mm Remington Golden Sabre"

Experiment

"Black Hills 77 Grain Sierra Match King"
"Hornaday 75 Grain TAP"
"Lake City 55 Grain"

Weapon "Bushmaster Carbon 15 pistol"

At any rate, Backyard Ballistics decided to test the "heavier is better" theory with regards to bullets. In my clearly non-scientific test, I used my Bushmaster Carbon 15 pistol, several phone books taped together, and milk jugs filled with water as targets.

The main question for this test was to see if the bullets would fragment at all coming from the super-short barrel. If bullets will fragment, then the super short design may hold some promise as a personal defense weapon.

The penetration depth and such will follow later.

The milk jug test ended pretty quickly with a Black Hills Match king zipping through all 3 jugs and shredding them rather soundly. Sorry, no pics.

On to the phone book test. I duct taped 2 phone books together. One bundle was about 3 inches thick, and the other was about 3.75 inches thick. After shooting cleanly through the smaller phone book set, I decided to put both of them together so I could have recoverable samples.

Results:

This is a layout of all the samples I recovered. At the top left, you have Lake City ammo. At the top right, you have 9mm JHP. The center are random fragments. The bottom left are the fragmented tops. The bottom right are the fragmented bottoms.

http://images5.theimagehosting.com/DCP_0223.jpg


9mm- Fairly disappoing in this test, as the neat mushroomed hollowpoints weren't to be had. I fired it out of my Steyr M9, but I presume the phone books were too dense and there was shredded paper clumped in the hollow point.  

http://images5.theimagehosting.com/DCP_0250.jpg

Lake City 5.56- Surprise, surprise! Lake city xm193 does not fragment coming out of a 7.5 inch barrel, but we knew this already. If you ever get attacked by a rabid pack of phone books, you better not be carrying 55 grain Lake city.

http://images5.theimagehosting.com/DCP_0228.jpg

This round didn't really do anything, although you can see from the tip there was some yawing going on.

http://images5.theimagehosting.com/DCP_0248.th.jpg

Black Hills Sierra Match King/Hornaday TAP- Ok, Here is why I am not a scientist, but rather an economist. I didn't have a good way of digging the rounds out of the phone books and putting them back together after firing each round, so I just fired a bunch of rounds into the phone books and collected the results. Plus, I didn't want one sample, but several so I could have a some depth of data to present.

Either way, I did recover several fragmented bullets from the phone books. The bullets split across the cannelure leaving the top, bottom, and either lead pieces or sometimes a solid lead core, so you are looking at at least 3 different pieces floating around in a person, but as you can see form the pile of random bullet parts, there will probably be 5 to 8 different fragments per bullet.

Random bullet fragments, jacket casings, etc...FYI, this is from several bullets, probably around 4 or 5 total bullets.

http://images5.theimagehosting.com/DCP_0252.jpg

Bullet tips found

http://images5.theimagehosting.com/DCP_0232.jpg

Another view, several had completely empty insides

http://images5.theimagehosting.com/DCP_0242.jpg

Bottoms- Off to the left, you can see some complete lead innards

http://images5.theimagehosting.com/DCP_0241.jpg

Top view of the bottoms

http://images5.theimagehosting.com/DCP_0239.jpg

I also found some really cool "yawing in action" bullets, where you can see the cannalure is clearly broken, but the lead is streached out still holding the pieces together.

http://images5.theimagehosting.com/DCP_0245.jpg

More Yawing in action

http://images5.theimagehosting.com/DCP_0246.jpg

Another view

http://images5.theimagehosting.com/DCP_0237.jpg

One more thing, about the reliability of carbon 15's, I fired more than 100 rounds total of various ammo without so much as a hitch. The weapon functioned flawlessly. I sent my Bushy back to the factory for some tweaking following some Jam o Matic action initially, but the weapon was smooth as butter. Bushmaster was also quick to respond, emailed me a 2 day overnight airbill from UPS, and had it back less than 5 days later. I also lubricated the charging handle as suggested here, and I had no problems what so ever.

From what I have heard, the feed ramps are really sharp and the rounds get hung up on there. Whatever they did worked, and I am a happy camper.

Phone books do not duplicate what goes on in flesh.  Pack the phone books in a cardboard box, and soak it in water, you'll have a better indication of real life performance.  You will not see expansion or the kind of deformation in wood or windshields that you will see in ballistic gel, wet phone books, clay, or flesh.

And you imply the bullet is effective only if it fragments.  The 5.56, as it yaws, turns and proceeds tail first, does pretty good damage like that.  You will note that many are bent, or "fishhooked".  That will do a lot of damage, too.

ok hears a question, so lets say if a head shot is achieved, from a 7 or 11 inch barrel, how far can  you make a kill at?  although some rounds may not fragment with shorter barrels a head shot will still drop them where they stand

Yeah, I wanted to have more of a "wet" test, and I figured a dry phone book is CONSIDERABLY more dense than a human body. I think the 9MM JHP failure to expand indicates this. My initial plan was to soak the phone books in the remaining water following the water jug test, but there wasn't much water or jug left after the initial shot...

I am thinking next time to take some newspaper, which is less dense than some phone books packed toegether, wet it down and put it in a box and see what happens. Since we know the Lake City won't fragment, although it will yaw some, I am going to focus more on the Hornaday,  Black Hills, and other heavier ammo. I am thinking 4 boxes, one where I fire 1 round into so I can look at the differences, and another where I fire 10 shots into, so I can better estimate the effect on the population.

I think people really, really underestimate the wounding potential for this weapon, assuming you use the appropriate ammo for it. Sure, the Hornaday and Black hills stuff is more expensive, but I wouldn't suggest shooting it as a training round. Stick to the cheap Lake City stuff for that. It wouldn't cost that much to have a couple mags worth, say 100 rounds.

I wanted to add I have a 1/9 twist.

As far as Maximum effective range, I am thinking of 150M max. I can't imagine how I would have to shoot farther than that with this weapon and 50-100M more of a working range. If I need to shoot more than 150, I DO need a full length rifle. For home defense/PDW, I think this is ideal.

Quoted: but will a 1/9 twist stabilize the 75-77 grain bullet?  You may have "fragmentation" because the bullet is keyholing and hitting the target sideways.  I was under the impression that 1/9 was good up until about 65 grain.  Above that you need a 1/7.

1/9 is fine for 77 grain bullets, but is the slowest twist you'd want for that.

Quoted: ok hears a question, so lets say if a head shot is achieved, from a 7 or 11 inch barrel, how far can  you make a kill at?  although some rounds may not fragment with shorter barrels a head shot will still drop them where they stand

You don't always have the ideal shot or the time to make it.

Here's what Bushmaster says. I was asking about 1/7 barrels in 7.5 inches. I haven't seen many.

"Craig,

Not at this time. The 1/9 will stabilize  between 40-75 grain. The 1/7 between 50-80 gr.

Look forward to your articles give me a heads up when they come out.



Thank you.
Harvey Macomber
Customer Service
Bushmaster Firearms
800-883-6229"

So, it looks like 77 grains is just above the stabilization threshold.

If you shoot into a 12-15 foot deep box of sand , they shread up...


They don't just TACO ...

try that one next time and you will get different results on what hapens to the bullet.

TACO? What results am I looking for?

the stabilization is a matter of luck, both my Bushys(14.5", 20" both 1/9) shoot the 75/77 grain ammo great, under an inch at 100 yards. others have had some problems in their rifles though.

If you so interested why didnt you just make uncalibrated 10% gelatin at least?

I was thinking sort of the same thing. With a 7 inch barrel, I don't expect to shoot at ranges further than 50-100M or so. I think at those close ranges it should be stable enough. It isn't like you are shooting a 40 grain bullet out fo a 1/7 or a 100 grain bullet out of a 1/12. The tolerancess are pretty close.

I was thinking of going to the store and getting a bunch of Jello and a few milk jugs, heh.

Quoted: I was thinking of going to the store and getting a bunch of Jello and a few milk jugs, heh.

I tried that once with some knox gelatin, but it never solidified.  I think it needed to be exposed to air, it was sealed in the jugs.

Made a big mess, maybe I just didn't do it right.

I'm just glad to here that there's another member of the Reliable Carbon Club(tm).

I don't understand what that un-scientific test was supposed to prove.

I took my Carbon 15 carbine out again 2 weeks ago. I put a little over 100 rounds of wolf and m193 and had zero problems. I'm happy with mine so far.

Quoted: I don't understand what that un-scientific test was supposed to prove.

If 77gr bullet would fragment if shot from a very short barreled AR.

At what distance did you shoot from?

It was pretty close distance, I'd say 50 feet or less. To reiterate for others, the goal was to see if heavier ammo would fragment reliably in an AR pistol. Some people in the pistol thread were saying how an AR pistol is just a waste of money/expensive toy.

I consider it a PDW, and I want to see if the bullets will fragment, thus increasing the wounding potential.

Uhm not to be a big meanie or anything, but 100 rounds reliablity does not make. Try firing through 5-6 30 round mags as fast as you can, then without letting the rifle cool, run your drills, shoot your targets, etc.  If your gun performs well that hot, then  you can say it's reliable. I've done this with my carbine and found some problems that needed correcting. Now she'll run the whole test just fine.

-sc

Quoted: I consider it a PDW, and I want to see if the bullets will fragment, thus increasing the wounding potential.

As a PDW, I think it will do fine, whether it fragments or not.  Would be good if you could chrono your loads, that would be very useful.  My guess is that they would be very favorable (ballistically) compared to many handgun cartridges, and specifically the 5.7x28.  

working off of what Bushy told me and other estimates, the velocity should be around 2200-2400 FPS or so out of the shorter barrel.