November 23, 2012

Silent But Deadly… No, Not Farts

I grew up in Texas, and my dad was a gun dealer.  He owned a shop and we spent many weekends either shooting or working gun shows.

So when Gunny Highway said, “This is the AK-47 assault rifle, the preferred weapon of your enemy; and it makes a distinctive sound when fired at you, so remember it,” in the movie Heartbreak Ridge, I knew exactly what he meant.  Guns do have distinctive sounds, and once you hear them, you can’t mistake them for anything else.

The reason for that noise is that most bullets make a sonic boom when they are shot, they quite literally break the sound barrier.  That crack you hear is a projectile traveling at over 1,100 feet per second.  And let me tell you from experience, they do sound different.  The 9mm Smith & Wesson I took my concealed carry permit class with sounds COMPLETELY different than the 30.06 Remington deer rifle my dad carried, and they both sound different than the Russian AK-47 a friend let me shoot once.

The one thing they all have in common is that they sound exactly like a bullet being shot. Kinda like you will never mistake the sound of a prairie rattler warning you off for any other noise, you will NEVER mistake the sound of a gun shooting for something else.

As you can imagine, this is a problem for Special Forces teams when they are trying to be sneaky in some foreign country.  So, the Special Operations Command, SOCOM, has been shopping around trying to find subsonic ammunition.  According to their latest round of small-business solicitations, the ammunition would provide “superior covert and stealth capabilities” for the military, police forces and Homeland Security.

The theory is that if you slowed down the bullet, say for rifles in the 5.56, 7.62 and .338 calibers, they wouldn’t break the sound barrier and that distinctive sound wouldn’t happen.  This would also mean not needing a sound suppressor, or what most folks would call “a silencer,” which everyone should know isn’t silent and is only good for a couple uses before you have to rebuild or replace it anyway.  They are bulky and of limited use, so not having to schlep them around would be a boon for the Special Forces teams.

This theory sounds pretty good, right?  Right!

Subsonic bullets do exist.  The Defense Department says they don’t have any “classified for use in the calibers provided by any DoD service.”  Which tells me they do have them, just not in the calibers used in high-powered sniper rifles, automatic machine guns, or any other really useful combat weapon size.

Special Forces teams have even been using the subsonic bullets that do exist since World War II in small caliber guns like .22 and 9mm pistols.  The problem is those large caliber, high-powered rifles they need in stealth situations.  Big beefy rifles and slow subsonic bullets do not get along very well.

There are a lot of trade-offs involved in slowing a bullet down enough to be silent.  The SOCOM solicitation notes that they “experience significant accuracy problems due to excessive deviations in velocity.”  That’s political talk for “can’t hit what they aimed at!”

Let’s get technical for a bit.

A subsonic bullet uses less gunpowder, or propellant charge, than a regular bullet does, and the bullet itself has to be heavier.  Remember when they took weight off the back axle of a Ford Mustang and goosed the engine up?  You got a really pretty car that fishtails if there is so much as a single raindrop on the pavement.  Same thing here. A heavier bullet with less “oomph” is less accurate, doesn’t have nearly the same kind of range, and “creates lower pressures which … makes it hard to get a clean burn of the propellant causing rapid fouling of the weapon.”

Lack of a clean burn is caused by a failure of obturation.  When a bullet is expelled through the barrel of a gun, it expands – obturates – to the size of the barrel.  This keeps it on target because it can’t wobble around, and prevents the gases which are pushing it through the barrel from getting ahead and melting to the inside of the gun.

If that happens, the melted leading can be difficult to remove.  If it isn’t removed, the weapon can be permanently damaged, causing misfires, backfires and jams.

The weight of the bullet is really important too.  Being either too light or too heavy can prevent obturation.  Subsonic bullets have a reputation for jamming in the weapon, which can be deadly in a firefight, just ask any Vietnam vet who had to use an M-16.  Jamming is bad, mmmkay?

The Pentagon has suggested building subsonic bullets with polymer casings instead of the brass or steel jackets used now.  They aren’t really specific about how this will work out, but the basic premise is that these casings would “produce a reliable and consistent powder burn.”  Since polymer obturates at lower pressures than brass or steel, it might be possible to shoot a heavier bullet and not trade off any accuracy or range.  At least in theory.

This is not the first time the DoD has looked for an answer to this problem of noise. Back in the late 1980s to early 1990s there was a project called the Advance Combat Rifle.  The Army poured nearly $300 million into it, looking for a replacement for those M-16s I mentioned earlier.

One rifle to come out of that project, the Steyr ACR, did use polymer bullets.  According to records though, it was wildly inaccurate due to the strength of the cartridges being inconsistent.  Maybe SOCOM can fix that problem, because we all believe that government designed products are high quality and consistent, right?

Personally, I think we need to train our Special Forces more in recon, stealth, and extraction techniques instead of worrying about how loud their weapons are.  I would much rather they carried highly accurate weapons and learned how to bug out better when the proverbial shit hits the fan.

Image Credit: DVARG / Shutterstock

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