Firearms and sound and recoil dampening

Some kind of rocket that starts out slow and builds up speed. This was tried with the Gyrojet pistol. https://en.wikipedia.org/wiki/Gyrojet

The Soviets had some sort of captive piston gun where the powder charge was retained in a pressure vessel and drove a captive piston which struck the projectile. I have no idea how well it actually worked but at least in theory it could completely contain the muzzle blast.

Recoil reduction is easy, just use a portion of the gas to drive an inertial mass in the opposite direction.

Roboss said:

without using subsonic rounds with supressors?

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Not unless you can change the physical properties of Air.

Things that move super sonically through air make a sonic boom.

Gunpowder DOES NOT "explode". Read some books.

Actually the captured piston rounds where in the US arsenal in the mid to late 1960s

"I canna change the laws of physics, Captain."

-kBob

Roboss said:

The hammer striking the primer, the explosion of chemical powder inside the chamber and then the sonic boom.

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The mechanical action of a firearm seldom exceeds 60dB.
The ignition of propellant withing the sealed firearm also has little sound impact.

The primary sound source is the release of propellant gasses after the projectile leaves the barrel. Those gasses expand rapidly on exit; they have high velocity, if little mass. That is the report, the "gun shot."
Those projectiles accelerated above the speed of sound will add the projectile's sonic boom to the noise generated. This is often referred to as the "crack" of the bullet.

This is not a simple calculus. Size of the charge, length of the barrel, mass of the projo, the MV & ME.

Recoil is just as complicated, too. Mass of the arm, MV projo mass; much of recoil is perceived by the shooter, too. And there's a component related to whether the reciprocating bolt (or carrier)--if the firearm is so equipped, strikes the end of the receiver on firing. (Eliminating this contact is possible, just at engineering and ergonomic cost; we see a number of arms using softer buffer materials to reduce this impact.)

Oh, and this is a hugely complicated topic upon which the entire firearms world has an opinion, often differing opinions upon. Actually, it's two topics, and they both generate disagreement (and occasional discord).

A note of caution--this can be as divisive as caliber wars or revolver vs. automatic.

To a small degree more efficient bullets have made it possible to help somewhat with sound and a lot with recoil. In 2020 a 9mm is every bit as effective as a 357 mag was in 1970 And a lot quieter. You'd still need a suppressor to get sound levels low enough to prevent hearing damage. But a 9mm round will damage your hearing less than a 357. You'll still go deaf, it'll just take more rounds.

In rifles more efficient bullets have allowed us to shoot smaller, more efficient cartridges with less recoil and still get the same performance on game. For example if we shoot an old school 180 gr RN bullet from a 300 WM at 3000 fps you'll get hit with 30-31 ft lbs of recoil. If we shoot a modern aerodynamic 180 gr bullet from a 30-06 at 2800 fps you'll get hit with 20-21 ft lbs of recoil. BUT... at only 75 yards the more aerodynamic bullet fired from the 30-06 will be moving faster, and hit harder than the 300 WM. Shoot the same aerodynamic bullet from a 308 and you'll get 15-16 ft lbs of recoil and the 308 will surpass 300 WM at about 175 yards, and widen the gap as range increases.

Granted, you can shoot those bullets in a 300 WM and really stretch downrange performance. But having the option of shooting a 308 with half the recoil of 300 WM and still get the same or better performance at 200 yards as our grandfathers did with a 300 WM is sort of a big deal.

This is a huge part of the reason why 6.5 CM has taken off. In a nutshell it offers the most performance for the least recoil. It is the smallest round that shoots bullets heavy enough and with the ability to penetrate deep enough on game like, elk, moose, bear, yet it does it with recoil not much greater than 243.

To a degree the same can be said of shotguns. For a lot of applications today a 20 ga is more than enough gun for jobs where a 12 ga was needed years ago. In other words we've started working smarter instead of just trying to muscle our way through problems.

Excellent points, @jmr40 . All very true.


None of which I would like to try inside!

https://armamentresearch.com/british-de-lisle-carbine-bolt-action-rifle/

The De Lisle is very nice, but subsonic. And boy would I like to have one!

How small would a projectile have to be before its sonic boom is inaudible to humans in the normal din of a room?
.40 caliber?
If stabilized and supersonic would it be effective?
(Actual repeating firearm, not shrapnel or flechettes.)

A very interesting question, @Roboss.

Demi-human said:

How small would a projectile have to be before its sonic boom is inaudible to humans in the normal din of a room?
.40 caliber?

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Not diameter, velocity.
.22RF is supersonic; .45acp is not.
Speed of sound (at sea level) is in the neighborhood of 1050fps.
Trans-sonic kicks in around 2750 fps (I may be wrong on that), but, usually where rifle rounds lose accuracy is as they slow below the speed of sound (this has more to do with how the airflow changes).

"Normal din of a room" varies a lot. 'Normal' conversation is around 60dB, noisy bar can get to 80-90dB (remember that decibels are measured logarithmicly, every 10 dB is a exponential, not decimal increase).
OSHA says that you are not allowed to expose workers to sounds over 140dB--there are far too many silencers advertised as "hearing safe" for being right at 140dB.
Typically, the pain threshold for humans is around 110dB.
Firearms run from 140 to 180dB.
With really good suppression, you can get firearms to 130-140dB. Some extreme designs, like, say Welrod, that will push down to the 110-120dB
That's 60dB louder than ordinary conversation, 64x more energy (10^6 more intensity).

CapnMac said:

Trans-sonic kicks in around 2750 fps (I may be wrong on that), but, usually where rifle rounds lose accuracy is as they slow below the speed of sound (this has more to do with how the airflow changes).

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2750 fps is in the range of MUZZLE velocity likely to remain supersonic at extended range, 600-1000 yards. Transonic is taken to start around 1200 fps and declining to 1000 or so; actual speed of sound at ambient conditions is not a sharp transition for a bullet.

A "gauss gun" would have potential for the least sound signature and recoil of any projectile weapon. No jet effect to add to recoil, no report of expanding gas (except for air forced out of the solenoid by the bullet.) Do you want flat trajectory and penetration or do you want to avoid a shockwave bark? Just turn the dial.

Power supply and cooling seem the greatest engineering challenges.
Jack Williamson assumed them solved in the Unitron pistol and E.E. Smith with "force field projection" on planet Osnome.

Roboss said:

If technology advanced far enough, how could we dampen the sound of a firearm low enough that it wouldnt damage hearing even when fired indoors without using subsonic rounds with supressors?

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CapnMac said:

Not diameter, velocity.

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Very true.
But, .40 caliber being about the thickness of a straight pin, would a very small supersonic projectile be able to be heard(under 40decibels), and still effective.(Kill a mouse.)

Let us remove the firearm. Somehow, it just works, and does so silently.

Would such a projectile still act as a proper bullet?


I guess I am asking the smallest limit on rifle thrown projectiles, and if their sonic crack was equally small enough not to be heard above normal room noise, however variable.

Same thing with recoil. I am aware that laws of physics cannot be denied but what could in the future allow firearms to punch with more force yet maintain low recoil

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Add a lot of weight; Newton cannot be denied

22CB is pretty quiet out of 24 inch barrel locking bolt gun.

My 27 inch Walther was very quiet with the paper box CCI 22 LR standard velocity as sold in the last century. For some reason the current stuff is not as soft.

I like to compare gun shot sound to popping the cork on champaign. The pressure in a champaign bottle is around 70-90 psi and the cork velocity is maybe 100-ish fps. That can make a surprisingly loud pop. Gun shot sound is the same principle but with much higher velocities and pressure. What would that champaign opening sound like if the pressure was several thousand psi?

I know that there has been work on reducing sonic boom noise for aircraft. I think NASA’s test aircraft are moving a bit slow for a rifle bullet and also wonder if that sort of shape would work in a projectile without a sabot.

Demi-human said:

But, .40 caliber being about the thickness of a straight pin,

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We have a units hiccup here, I think. My backhoe had some connector pins that were 0.40" diameter; that's 4/10 inch, or about 10mm. The bucket pins were 50 and 55mm.

Straight pin, if memory serves runs about 0.5mm (±0.0196") and perhaps half a gram. So, it will accelerate quickly, but lose momentum as quickly. There's a side issue in just how you apply the force to a small thing to bring it to the desired velocity. Our current method is to use a fixture to grasp the projectile. We use the French, "sabot" (shoe) to label this fixture.

Physics is cruelly exacting in these things. There are mass and diameter ratios which want preserving, you simply cannot put a straight pin in a 100mm sabot and expect super performance. There's some issues with getting pointy things down below the turbulent air flows associated with Mach curves (at least that what by buddy the rocket scientist--works on hypersonics for LMM--tells me).

Another take on quiet shooting.

CapnMac said:

We have a units hiccup here, I think.

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“.40 caliber”, not “40 caliber”.

CapnMac said:

So, it will accelerate quickly, but lose momentum as quickly. There's a side issue in just how you apply the force to a small thing to bring it to the desired velocity.

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CapnMac said:

Physics is cruelly exacting in these things. There are mass and diameter ratios which want preserving, you simply cannot put a straight pin in a 100mm sabot and expect super performance. There's some issues with getting pointy things down below the turbulent air flows associated with Mach curves (at least that what by buddy the rocket scientist--works on hypersonics for LMM--tells me).

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This is exactly what I mean.

748 said:

22CB is pretty quiet out of 24 inch barrel locking bolt gun.

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Not when fired inside a garage ......Even the little bb caps i found in a pile of old stuff are loud enough to be uncomfortable.
Colibris arnt bad, less loud (and less accurate/effective) than my shrouded but baffle-less air rifle.

If technology advanced far enough, how could we dampen the sound of a firearm low enough that it wouldnt damage hearing even when fired indoors without using subsonic rounds with supressors?

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If the building has enough room, sounds like a metro gun tube would be the ticket.

jmorris said:

If the building has enough room, sounds like a metro gun tube would be the ticket.

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Do you touch them with it?