Tuesday, April 12, 2016

Newbie's Guide to Guns, Part 2: Rifle and Pistol ammunition

We saw last time that caliber is a lot more complicated than the textbook definition of "diameter of the barrel in inches": different calibers are actually different specifications of the size, shape, and weight of the bullet itself as well as the powder charge.

One of the places this is most clearly seen is the comparison between pistol and long rifle ammunition. We recall from last time that a 9mm bullet is really a .38 caliber. That means that a .308 Winchester is really a lower caliber than a 9mm Luger.  But  a .308 packs a whole lot more punch than a 9mm Luger.  The difference is quite clearly seen if we look at the actual cartridges.

The 9mm Luger is a reasonably short round

The .308 is a great deal longer

I can't find a picture of them side-by-side, so we'll have to look carefully: although the .308 bullet and the 9mm bullet are approximately the same diameter,  the 9mm round looks much larger in proportion to the cylinder. That's because the 9mm Luger is 19mm long (hence the designator "9X19mm" while the .308 Winchester is 51mm long (recall a .308 Winchester is almost identical to the 7.62X51mm NATO round).

The difference between the lengths of the two cartridges indicates the relative strengths of the powder charges. Not only is the .308 round a whole lot heavier than the 9mm round, it is packaged with a whole lot more powder.

This exemplifies the main difference between pistol and long rifle ammunition: rifle ammunition generally packs a lot more "punch".  The 9mm Luger round is expected to have a muzzle velocity in the neighborhood of 370 m/s (somewhere around 1200 ft/s), the .308 is expected roughly to double that with speeds around 800 m/s.  If we recall our high school Physics class, we'll remember that kinetic energy is proportional to the square of the velocity, so the .308 carries about four times the energy of the 9mm, without taking into account the difference in bullet mass.  We'll discuss that in more detail later.

There are some rifles that use pistol ammunition, like lever guns chambered in .357 Magnum or .44 Magnum. Although they use the less powerful pistol ammunition, they still tend to get a lot more energy out of those same rounds than a pistol would. Why is that?

It actually comes down to the length of the barrel.  When a gun is fired, the bullet is forced down the barrel by the expanding gasses produced by the burn of the gunpowder. Once the bullet exits the barrel, it's no longer being pushed by the burn of the powder, and will begin to decelerate immediately because of air resistance. If two identical cartridges are fired from two different guns, the one with the longer barrel accelerates for a longer distance, exiting the barrel with a higher speed. So the longer barrel almost always means a faster (i.e. more energetic) bullet.

I suppose the effective limit of this rule of thumb would be the maximum volume of the expanding gasses. In other words, the powder doesn't expand to an infinite volume when it burns. Whatever the maximum volume of the powder charge's burn is, that's when a bullet would stop accelerating down a barrel. If the barrel's volume were larger than that expansion, then we'd expect the bullet to decelerate rapidly in the barrel due to the friction of the barrel. But I'd expect a barrel that long would be impractical to carry.

So there are two main reasons a rifle hits harder than a pistol: rifle ammunition is packaged with a whole lot more gunpowder to push those bullets, and rifle barrels are longer, so that even when the powder charges are identical, bullets accelerate longer in rifles and thus come out of the muzzle with a lot more energy.

So the next time you hear someone talk about a .50 caliber pistol, don't assume it's more powerful than a .30 caliber rifle. It probably isn't. Even though it might have a ridiculously large bullet, it probably has significantly less powder, and it almost certainly is coming from a shorter barrel.

Sunday, April 10, 2016

Newbie's Guide to Guns, Part 1: Caliber

I first started shooting as a teenager, in Air Cadets.  We were trained on Lee-Enfield rifles (probably WW2 surplus) [re]chambered in .22LR. Those were heavy rifles for a new shooter! If I recall correctly, they weighed in around nine pounds.

One thing I had trouble grasping for many years was the names of firearm calibers. It seemed to me the caliber names were at best inaccurate, at worst completely deceptive. So let me help dispel the mystery...

A firearm's caliber is named for the diameter of its bullets. So a .22 caliber rifle has a barrel .22 inches in diameter. Similarly, a .50 caliber has a half-inch barrel diameter.  Unfortunately, that's only really theoretically true. Things get a lot more complicated right out of the gate, and we'll look at that.

I suppose in the days of smooth bore muskets, the barrel diameter told the whole story. The bullets were essentially spheres of lead. Given that the density of lead is a constant, and the volume of a sphere is strictly a function of radius, barrel diameter completely described those older bullets.

These days it's a lot more complicated. We now use cartridges that contain both the actual bullet and the powder charge: so we need to describe not only the bullet, but how much powder is behind it. And since we now use non-spherical bullets, the diameter doesn't tell the whole story.

Now we describe bullets by their caliber (diameter) and their weight. Bullet weight is measured in grains, one grain weighs 1 seven-thousandth of a pound. So if you're shooting 115gr 9mm Luger ammunition, you're shooting bullets that weigh 115 grains, or 0.26 ounces, or 0.016 pounds. In other words, they have a mass of 7.37 grams.

But unless you're just buying bullets (for example, you're reloading), you're not buying just the bullet, but the cartridge it comes in. This gets even more complicated, because the size and shape of the cartridge is at least as important as the caliber of the bullet. Guns are manufactured for a specific cartridge, and in general it's a really bad idea to try and use a different type of cartridge in there.

Cartridges are named by many different conventions, and it's not always easy to interpret what those names mean.  When I was small, hunters would talk about their "thirty odd six" rifle, and I had no idea what that meant. What they were really saying was "thirty-ought-six", or ".30-06".  This is the cartridge the U. S. Army adopted in 1906, and it's a .30 caliber. So it's the .30 from "ought six", or ".30-06".

Many cartridges are named for their original manufacturer. Savage Arms invented the popular ".300 Savage" round, a .30 caliber cartridge for the rifles they manufactured. Since Winchester invented the ".30-30", sometimes those are called ".30 Win" or even ".30 WCF" (meaning .30 caliber Winchester center-fired).

I remember growing up, hearing about a "thirty, thirty Winchester".  That is, a Winchester rifle that takes".30-30" cartridges. The ".30-30" means a .30 caliber bullet with 30 grains (0.069 ounces) of [black] powder. Similarly, a ".45-70" is a .45 caliber bullet with 70 grains of powder.  Both those cartridges come from the end of the 19th Century, when the U. S. Government designated cartridges by their caliber and powder charge.

A lot of rifles are chambered in ".308 Win", or the .308 caliber Winchester cartridge. Military rifles might use a "7.62X51mm NATO" cartridge, which is almost exactly the same thing as the .308. If you do the math, you'll find 7.62 mm is .30 inches.  Along similar lines, the AK-47 shoots "7.62X39mm", or a .30 caliber cartridge that's 39mm long.

There are other designators that are used. "Magnum" means over-sized, so when someone talks about a ".357 Magnum", they are referring to a cartridge with a .357 caliber bullet that's "oversized", which means it has too much powder.  You can also buy ".44 Magnum" or even ".50 Magnum" guns.

Probably the hardest thing for me to understand about ammunition was that the names are really only kinda-sorta accurate. Virtually every ".357 Magnum" will shoot ".38 Special" as well. I never understood that, as .357 inches differs significantly from .38 inches. It turns out the .357 Magnum and the .38 Special have the same diameter: .357 inches.  The .38 Special was apparently marketed as .38 caliber, because the cartridge itself was .38 inches in diameter, even thought the bullet was only .357 inches.

Marketing is probably the hugest driver for cartridge names. If you do the math, you'll see that .38 inches is 9mm; but a "9mm" round is quite different from a ".38 caliber" round: they're the same measurement, but the names imply very different specifications.  When someone says they have a "9 mm" pistol, they generally mean it shoots "9mm Luger" cartridges. If someone has a ".38", they generally mean  a ".38 Special".

In the end, when I was told many years ago that "caliber" means "diameter in inches", that's not really the whole story. Cartridge names are really a sort of branding: they refer a specific, detailed design. Diameter is a huge part of that, but there's a lot more to it than just bullet diameter.

Monday, April 4, 2016

Can-Am Pie

Several months ago we were eating butter tarts, and someone suggested it might be interesting to mix butter tarts with apple pie.

I suppose this pie might be a metaphor for our family: Butter tarts are the quintessential Canadian dessert, and apple pie is as American as... well, apple pie. So I'm calling this one "Can-Am pie".

I started with four large Granny Smith apples, peeled and cored.

I squeezed half a lemon over them to keep them white-ish.

Then I made some butter tart filling.

Butter tart filling is a mixture of butter, eggs, brown sugar, and corn syrup.  Like all Canadians, I have a family recipe for butter tarts, but this one was just a recipe I got out of a cook book.

One of my current fascinations is raised pie, so I decided to put this one in a hot water pie crust. I used a spring-form pan to shape the pie.

I poured the entire batch of butter tart filling into the crust, then put the apples on top, sprinkling them with cinnamon and white sugar:

I covered the pie, then baked it for 45 minutes. After 45 minutes, I took the pie out of the pan and brushed it all over with egg wash, then baked for another 15 minutes.