Ballistics by the inch

‘Rifleshooter’ does .223/5.56 chop tests down to 6″

A very nice companion to our .223 chop tests:

223 Remington/5.56mm NATO Barrel length versus Velocity- Short Barrels- 6 to 14 inches

In 223 Remington/5.56 NATO, velocity versus barrel length: A man, his chop box and his friend’s rifle, we cut the barrel of a factory Remington 700 chambered in 223 Remington back one inch at a time and recorded the average velocity for four different 223 Remington and 5.56mm NATO cartridges.  The data set generated from that post provided imperial values for muzzle velocities from 26″ to 16.5″.  A few readers suggested mounting the barrel in a pistol and continuing the test for shorter barrels- we liked the idea.  In this experiment, we gathered data using the same barrel from the first 223 Remington/5.56mm NATO experiment (on a pistol action), with the same four kinds of ammunition from 14″ to 6″.

 

Good protocols, good documentation, good data. And between his different tests, he covers a wider range of barrel lengths than we did, and has some different loadings — so what’s not to like? Go check it out, and bookmark it to share with others!

 

Jim Downey

November 29, 2015 Posted by | .223, Data | , , , , , , , , , , | 1 Comment

Lucky seven.

Thanksgiving weekend 2008, we launched the BBTI website and blog. So while the 28th is the actual anniversary, I tend to think of the start of this journey on Thanksgiving each year.

Seven years. Wow.

And in that time so much has changed. As I’ve noted previously, BBTI has become a standard reference world-wide, and I think that we’ve actually helped create some changes in how ammo manufacturers market their products, providing customers with more reliable & useful information.

But there’s so much more which has come about because of BBTI. I’ve met and made friends with a lot of people. I’ve had interesting discussions & correspondence and learned an incredible amount from people who are much more knowledgeable than I am. People from almost every walk of life, and from all around the world. It’s been fascinating.

In my traditional year-end review I’ll get into all the numbers, but it has been a very good year in terms of visitors to the BBTI page and this blog. So for now I’ll just repeat what I said last year:

Thanks to all who have cited us, written about us, told their friends about us. Thanks to all who have taken the time to write with questions and suggestions. And thanks to all who have donated to help offset the ongoing costs of hosting and testing — it makes a difference, and is appreciated.

Cheers!

 

Jim Downey

November 26, 2015 Posted by | Data, Discussion. | , , , , , , , , | Leave a comment

Velocity is great, but mass penetrates.

OK, kiddies, it’s time for SCIENCE!

Ballistic science, specifically. I promise to keep the math to a minimum, because I don’t like it much, either. Jim Kasper is the one who thinks in terms of equations, not me.

If you look at any of the various pages for test results on BBTI you will see that each caliber/cartridge also has a link for a Muzzle Energy (the kinetic energy of a bullet as it leaves the muzzle of a gun) graph for that set of results. That’s because Muzzle Energy can also give an idea of the effectiveness of a given ammo, since it is a calculation of both the weight of a bullet as well as the velocity it is traveling. This calculation, specifically:

E_\text{k} =\tfrac{1}{2} mv^2

Here’s what that says in English, taken from the explanation that goes with that image on Wikipedia:

The kinetic energy is equal to 1/2 the product of the mass and the square of the speed.

In other words, you multiply the weight of the bullet times the square of the velocity, then take half of whatever number you get. And that gives you the Muzzle Energy, usually (as on our site) expressed in foot-pounds of energy.

So there are two ways you can change the result: change the amount of weight, or change the amount of velocity.

But since it is the square of the velocity (the velocity times itself), changes to the velocity have a larger impact on the final amount of Muzzle Energy. That’s the reason why how the velocity changes due to barrel length is such a big deal, and why we’ve done all the research that we’ve done over the last seven years.

But while Muzzle Energy gives you a good way to compare the power and potential effectiveness of a given cartridge as a self-defense round, there are a couple of other factors to consider. A couple of VERY important factors.

One is the shape and composition of the bullet itself. There’s a very good (surprisingly good, in fact — I heartily recommend you read the whole thing) discussion of the basic shapes and how they interact with the human body in this online teaching tool intended for medical students. The relevant excerpt:

Designing a bullet for efficient transfer of energy to a particular target is not straightforward, for targets differ. To penetrate the thick hide and tough bone of an elephant, the bullet must be pointed, of small diameter, and durable enough to resist disintegration. However, such a bullet would penetrate most human tissues like a spear, doing little more damage than a knife wound. A bullet designed to damage human tissues would need some sort of “brakes” so that all the KE was transmitted to the target.

It is easier to design features that aid deceleration of a larger, slower moving bullet in tissues than a small, high velocity bullet. Such measures include shape modifications like round (round nose), flattened (wadcutter), or cupped (hollowpoint) bullet nose. Round nose bullets provide the least braking, are usually jacketed, and are useful mostly in low velocity handguns. The wadcutter design provides the most braking from shape alone, is not jacketed, and is used in low velocity handguns (often for target practice). A semi-wadcutter design is intermediate between the round nose and wadcutter and is useful at medium velocity. Hollowpoint bullet design facilitates turning the bullet “inside out” and flattening the front, referred to as “expansion.” Expansion reliably occurs only at velocities exceeding 1200 fps, so is suited only to the highest velocity handguns.

Now, while that last bit about needing to exceed 1200 fps may have been true, or a ‘good enough’ approximation a few years ago, it isn’t entirely true today. There has been a significant improvement in bullet design in the last two decades (and these innovations continue at a rapid pace), so that there are now plenty of handgun loads available which will reliably expand as intended in the velocity range expected from the round.

The other REALLY important consideration in bullet effectiveness is penetration. This is so important, in fact, that it is the major criteria used by the FBI and others in assessing performance. From Wikipedia:

According to Dr. Martin Fackler and the International Wound Ballistics Association (IWBA), between 12.5 and 14 inches (318 and 356 mm) of penetration in calibrated tissue simulant is optimal performance for a bullet which is meant to be used defensively, against a human adversary. They also believe that penetration is one of the most important factors when choosing a bullet (and that the number one factor is shot placement). If the bullet penetrates less than their guidelines, it is inadequate, and if it penetrates more, it is still satisfactory though not optimal. The FBI’s penetration requirement is very similar at 12 to 18 inches (305 to 457 mm).

A penetration depth of 12.5 to 14 inches (318 and 356 mm) may seem excessive, but a bullet sheds velocity—and crushes a narrower hole—as it penetrates deeper, while losing velocity, so the bullet might be crushing a very small amount of tissue (simulating an “ice pick” injury) during its last two or three inches of travel, giving only between 9.5 and 12 inches of effective wide-area penetration.

As noted above, the design of the bullet can have a substantial effect on how well it penetrates. But another big factor is the weight, or mass, of the bullet relative to its cross-section — this is called ‘sectional density‘. Simply put, a bullet with a large cross-section and high mass will penetrate more than a bullet with the same cross-section but low mass moving at the same speed. It isn’t penetration, but think of how hard a baseball hits versus a whiffleball moving at the same speed. They’re basically the same size, but the mass is what makes a big difference. (See also ‘ballistic coefficient‘).

With me so far?

OK, let’s go all the way back up to the top where I discussed Muzzle Energy. See the equation? Right. Let’s use the baseball/whiffleball analogy again. Let’s say that the baseball weighs 5.0 ounces, which is 2,187.5 grains. And the whiffleball weighs 2/3 of an ounce, or 291.8 grains. A pitcher can throw either ball at say 60 mph, which is 88 fps. That means (using this calculator) that the Kinetic Energy of a baseball when it leaves the pitcher’s hand is  37 foot-pounds, and the whiffleball is just 5 foot-pounds. Got that?

But let’s say that because it is so light, the pitcher can throw the wiffleball twice as fast as he can throw a baseball. That now boosts the Kinetic Energy of the whiffleball to 20 foot-pounds.

And if you triple the velocity of the whiffleball? That gives it a Kinetic Energy of 45 foot-pounds. Yeah, more than the baseball traveling at 88 fps.

OK then.

Now let’s go look at our most recent .45 ACP tests. And in particular, the Muzzle Energy graph for those tests:

What is the top line on that graph? Yeah, Liberty Civil Defense +P 78 gr JHP.  It has almost 861 foot-pounds of energy, which is more than any other round included in those tests. By the Muzzle Energy measure, this is clearly the superior round.

But would it penetrate enough?

Maybe. Brass Fetcher doesn’t list the Liberty Civil Defense +P 78 gr JHP. But they did test a 90 gr RBCD round, which penetrated to 12.0″ and only expanded by 0.269 square inch. Compare that to the other bullets listed on his page, and you’ll see that while the depth of penetration isn’t too bad when compared to other, heavier, bullets, that round is tied with one other for the least amount of expansion.

Driving a lightweight bullet much, much faster makes the Muzzle Energy look very impressive. Just the velocity of the Liberty Civil Defense +P 78 gr JHP is impressive — 1865 fps out of a 5″ barrel is at least 50% faster than any other round on our test results page, and almost 400 fps faster than even the hottest of the .45 Super loads tested.

But how well would it actually penetrate? Without formally testing it, we can’t say for sure. But I am skeptical. I’m not going to volunteer to getting shot with one of the things (or even hit with a whiffleball traveling 180 mph), but I’m also not going to rely on it to work as it has to in the real world, where deep penetration is critical. I want a bullet with enough punch to get through a light barrier, if necessary. Like this video from Hickok45, via The Firearm Blog:

Personally, I prefer a heavier bullet. Ideally, I want one which is also going to have a fair amount of velocity behind it (which is why I have adapted my .45s to handle the .45 Super). All things being equal (sectional density, bullet configuration and composition), velocity is great, but mass is what penetrates.

Jim Downey

November 8, 2015 Posted by | .45 ACP, Data, Discussion. | , , , , , , , , , , , , , , , , , , , , , , , , , , , | 3 Comments

Dealing with power.

About 40 years ago, when I was an idiot teenager (yeah, I know — redundant, particularly in my case), we got this ’48 Willys Jeep. Since the engine was shot, we dropped an Olds V-6 in it. This was, essentially, like strapping a rocket to a skateboard. And it was too much power for idiot teenage me to handle.  Twice I snapped the driveshaft on the thing, just dumping the clutch too damned quickly. Twice. My uncle (who I lived with) was certain that I had been racing or something similar. The truth was, I didn’t even have that much of an excuse; I had simply goosed the engine too much and popped it into gear too fast. The original driveshaft just couldn’t handle that much of a power spike.

This is kinda what happens to your poor .45 ACP firearm when you decide to run some .45 Super through it.

With the Jeep, we wound up putting a more robust driveshaft in it. And I learned that if I wanted to keep driving it, I needed to be less of an idiot.

This analogy holds to how you should approach handling .45 Super power out of your .45 ACP gun. Chances are, very occasional use of these much more powerful loads won’t cause any problem in a quality, modern-made firearm. But if you’re smart, you’ll either greatly limit how many times you subject your gun (and your body) to that amount of power, or you will take steps to help manage it better and extend the life of your gun.

Typical ‘standard’ (non +P) .45 ACP loads tend to have a maximum pressure of between say 15,000 PSI and about 18,000 PSI. When you get past that, you get into ‘over-pressure’, or +P territory, up to about 23,000 PSI. This is the range most common modern firearms are built to handle safely.

But .45 Super generates more chamber pressure than that. How much more? Well, it’s a bit difficult to say, since there is a surprising dearth of data readily available. Neither my 49th Edition of Lyman’s Reloading Handbook nor my 13th Edition of Cartridges of the World have data for the .45 Super. Real Guns has some reloading formulas for .45 Super which give results consistent with our tests, but there are no pressure specs listed. Hodgdon Reloading has some pressure specs (in C.U.P.), but all their listed results for .45 Super are well below what our tests results were. Wikipedia lists .45 Super as having a maximum pressure of 28,000 PSI, and given that .460 Rowland is usually considered to run 35,000 – 40,000 PSI, that is probably in the correct ballpark.

I have written previously about converting a standard Glock 21 from .45 ACP over to .460 Rowland, and what is involved with that. Specifically, a new longer barrel with a fully-supported chamber which accommodates the longer case of the .460 Rowland, a 23 pound recoil spring, and a nice compensator to help tame the recoil. I also changed out the magazine springs, using an aftermarket product which increases the spring power by about 10%. This is because even with the other changes, the slide still moves much faster than with .45 ACP loads, and the increased mag spring power helps with reliability in feeding ammo. But even with all of that, shooting full-power .460 Rowland loads tends to cause damage to my magazines (as seen in the linked post).

Do you need to do all that in order for your firearm to handle frequent use of .45 Super loads? Well, I think that if you want to use a .460 Rowland conversion kit, it *will* tame the amount of recoil more than enough, but I don’t think that it is necessary to go quite that far. I should note that I have now run several hundred .45 Super loads through my Glock 21, and the gun has operated flawlessly — WITHOUT any damage to the magazines.

Converted G21 on left, G30S on right.

Converted G21 on left, G30S on right.

Rather, I think that the smart thing to do is to start off with going to a heavier recoil spring, perhaps swapping out a metal guide rod for a plastic one (if your gun comes with a plastic guide rod). Stronger magazine springs are probably still a good idea, to aid with reliable feeding. If suitable for your gun, add in a recoil buffer. These are the steps I have taken with my Glock 30S, and am planning for my Beretta Cx4 Storm. So far I have put a couple hundred .45 Super loads through the G30S with this configuration, and it has operated without a problem — again without any damage to the magazines.

As I said in my previous blog post, I still think that the .460 Rowland is a hell of a cartridge. But I think that the .45 Super offers almost as many advantages to the average shooter, with less hassle. I would still recommend that anyone who intends on shooting more than the very occasional .45 Super loads out of their gun consider making some simple changes to handle the additional power and extend the life of their gun. Don’t be like the idiot teenage me; deal with the power intelligently.

 

Jim Downey

 

 

November 1, 2015 Posted by | .45 ACP, .45 Super, .450 SMC, .460 Rowland, Data, Discussion., Links | , , , , , , , , , , , , , , , , , , , , , | 5 Comments