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Issa and I saw Inception last night. I enjoyed it immensely, and was glad to have seen it in the iMax theater, where the picture quality (specifically, black levels and overall screen contrast) seemed higher than it would have been in a non-iMax theater. For $16 a ticket, it better be good, and it was.

Concessions Hawkers

The only low point of the experience was the concessions hawkers who came into the theater before the trailers began and tried to sell us candy and such. It would be one thing if they said, “Hey, if you skipped concessions because of the lines, here’s your chance,” and stopped there, but it really came off as a hard sell. It felt embarrassing for them, and it was awkward for me to have to keep ignoring them, and it really disrupted the “movie bubble” that I like to imagine myself in going into a theater experience.

Recognizing Guns Instantly

No spoilers here, so don’t worry.

In the opening scene of the movie, the main character’s shirt is lifted and it is revealed that he has a pistol stuck in the back waistband of his pants. The image below is from a crappy vid-cam version of the film that I downloaded specifically so I could get a screen-cap of the shot in question, so you can see how much of the gun was revealed. It looks like shit, but you get the idea.

Even from the little bit of the backstrap, beavertail, and slide that was revealed, I instantly recognized it as a Px4, the same gun I have. It’s funny to me how firearms can be extremely distinctive based on very non-specific characteristics. Issa and I have had conversations where I’ll show her, say, a Beretta 92 and a 1911, and she’ll say, “They look the same to me,” and it seems to me like I could tell them apart at 100 yards, in the dark.

Sliencers and Caliber

The Px4 comes in calibers 9mm, .40, and .45. I wasn’t surprised to hear that the firearm used in the movie was .45, because it was suppressed. Here’s why.

The laws of physics apply to bullets the same way they do to anything else. There is a three-way inverse relationship between the speed of the bullet at the muzzle, the weight of the bullet, and the pressure in the chamber and barrel. Larger calibers have more mass, therefore it requires more pressure to drive them to higher speeds, which makes for more volatile, heavier, more expensive guns. Therefore, larger calibers tend to move slower. Interestingly, this does not necessarily mean that they sacrifice impact energy, since kinetic energy equals 1/2 mass times velocity squared and momentum equals mass times volume, some loss of velocity can be made up for by the increased mass. Additionally, larger calibers make bigger holes, even if they’re going slower. In other words, don’t let the fact that a .45 is going slower than a 9mm fool you into thinking there’s anything wrong with the .45.

What does all this have to do with suppressing the sound of a gunshot? A gunshot consists of several different components. The major component is the expansion of hot gasses that follow the bullet out of the muzzle. This is the part that a suppressor takes care of. Most handgun and rifle rounds are also supersonic, however, and for them there is also a miniature sonic boom that contributes a not-insubstantial amount of noise. For example, 9mm pistol rounds have a nominal muzzle velocity of about 1200-1500 f/s. The nominal speed of sound is 1125 f/s.

In this video (embedding disabled, so you’ll have to click through), an AR-15 is fired both with and without a suppressor. The sound that you hear with the suppressor on is the sonic boom caused by the bullet breaking the sound barrier.

http://www.youtube.com/watch?v=vvQUhzMHk98&NR=1

If you’re thinking that the suppressed .223 sounds a lot like a .22LR, that’s because a .22LR has such a small amount of powder that its primary sound component is the sonic crack, so a suppressed .223, which is all crack and no boom, sounds pretty much the same.

The sonic crack can be mitigated by simply reducing the amount of powder in the casing to reduce the velocity of the rounds below the speed of sound, but that requires either hand-loading your own cartridges or buying special cartridges intended for use with a suppressor. It’s more common to simply choose a caliber whose nominal velocity is already below the speed of sound. This avoids the potential loss of potency involved with down-loading a caliber designed for higher speed, as well as the potential difficulty involved with using specialized ammunition. With a nominal muzzle velocity of about 800 f/s, .45 is one of the only common handgun calibers that fits that bill.