A question about rifle sound suppression.

C

chris in va

New member
I spend too much time thinking about 'what if'.

Say there's a rifle barrel at 20". There's a loud report due to gas expansion at the muzzle. Traditionally suppressors have been used to drop the decibels down a bit.

But what would happen if a slightly larger diameter extension was screwed on the end, say...3' long. Or 20'.:eek:

At what point would the excess gas fill said cylinder and render the gun 'silent', save for the supersonic bullet shockwave?

Slo-mo video shows powder gas expanding a few feet past the muzzle. I guess that's what I'm driving at.
 
The extension would need to be so long that the bullet would strike the 'extension' due to recoil. (Unless it was not on the bore axis. In which case, it would need to be shaped as a progressively tightening arc.)
 
I would suspect that the undiverted gas in a slightly larger than bore cylinder would destabilize the bullet as it rushed past causing the bullet to strike the walls.

You could experiment until you found a diameter that would work, but at the end of the day, it would be accomplishing the same thing as a supressor much less efficiently.
 
The hole would need to be long enough to let bullet and gas to exit at the same time. It's the gas exiting 2 to 4 times faster than the bullet does that makes the sound pressure wave that's so much louder than the crack of the bullet's sonic shock wave.
 
But what would happen if a slightly larger diameter extension was screwed on the end, say...3' long. Or 20'.
Click to expand...

I'm no accoustics expert but as I understand it,

That wouldn't be the best way. You'd want a sudden, large volume for the gases to expand into and surround that with sound deadening material. I can't find a reference to it but I remember seeing a muffler design that was supposedly very effective, I can't even remember what it was for.

Basically like this, although there's obviously more to it than the shape:

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If the volume of the chamber is enough that the gases will expand and reach equilibrium temperature, the noise would be almost completely contained.

Of course, even if it worked, it'd be useless on a firearm because you couldn't aim.:D
 

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Brian Pfleuger said:
I can't find a reference to it but I remember seeing a muffler design that was supposedly very effective, I can't even remember what it was for.

Basically like this, although there's obviously more to it than the shape:
Click to expand...

IIRC, rather than being packed with restrictive sound deadening, those mufflers contained baffles that were supposed to offset the sound waves. Waves are additive, so if they're in syn, their peaks add to 2x. The baffles were designed so 1 wave is impeded by half a cycle, so, at the end of the muffler, the peak of 1 wave overlapped the trough of the 2nd, netting a "zero" sound wave.

As mufflers, they were so-so. Likely too many variables (engine size, RPM, exhaust gas temp & speed, etc) to get the baffles just so. Fewer variables in a rifle shot, so if they were tunable, such a design might work better on rifles.
 
There are some good suppressors out there now. I have seen .300 sub-sonic black out on bolt action that sounded like a high power air rifle. I have seen 5.56 ar's, running supersonic, that the action working was louder than the report.
 
As I understand it, "silencers" (suppressors) work because they "slow down" the escaping gas, by allowing it to expand, and making it go through baffles or some kind of other material.

While a larger diameter pipe on the end of the barrel might reduce the sound level at the shooter's ear a measurable amount, it doesn't slow the gas down, much. And the "heard/felt" reduction in muzzle blast may be due more to the muzzle now being further from the ear due to the length of the added "pipe", more than from its diameter.

Also be VERY aware that any device that is intended to reduce the sound of a firearm's discharge falls under several Federal and state laws, and is illegal to make, or posess, without proper govt approval, BEFORE you obtain the device.
 
I'm sure that does have some effect. It is, however, working with a cartridge that generally only operates between 11,500 psi and 13,000 psi in a .63 to .74 caliber barrel.
The volume needed for the gasses to expand into, to diminish the report, changes substantially when you start talking about something like a .30 caliber barrel with a cartridge running 45k to 65k psi.
 
44 AMP is right. The earlier suppressors slowed down the gas. Material really had nothing to do with it. Suppressors for rifles were huge. I am going back 30+ years. When I see suppressed guns on the news now, I can not believe how small they are now.
 
Basic priciple of suppression is...

COOLING!

Reducing the heat of muzzle gasses reduce the report.

The snap of the bullet passing is due to exceeding the MACH 1 level,

A .22LR has a very sharp snap passing over head.

LEO is now using sound detion for the report and bullet passage signature for

high-lighting location of incidents.
 
What the OP is talking about is called a "bloop tube", they were relatively common years ago. They do not reduce report so much as redirect it, if you are out in front of the rifle it is still very loud, but beside and behind the rifle it is quieter (kind of the opposite effect of a muzzle brake). But there are technical issues with them, most notably that the diameter of the tube has to allow room for the gas to expand without the shock wave upsetting the bullet flight. And since the move for years was towards shorter and shorter rifles, adding a couple of feet of tube to the front of the barrel was not that great of an idea.

The extension on the shotgun shown above is called a "metro tube" and is designed to quiet down shotgun loads for use in areas where noise would be unwelcome (like metro areas). They are legal according to ATF since they are not designed to reduce sound, that is a side-effect.
 
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