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el cañón de la combustión de 55mm

Built a combustion cannon? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
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Unread postAuthor: jackssmirkingrevenge » Wed Nov 26, 2008 1:38 pm

Radiation wrote:The problem is that the gun you referenced is an airgun.


The "captive piston" cartridges mentioned above are all power-burning firearms, I don't know where you got the airgun from?

It is more silent naturally.


That depends heavily on the airgun. If you've ever been next to one of these when fired without a silencer, it's even louder than a rimfire. The same is true of most high powered air rifles. Silencing an airgun is actually a much more difficult proposition as the pressure of the gasses is not the result of the temporary heat derived from a chemical reaction, but mechanical compression.

With a combustion based gun the only way to silence the sound is by (as you said) giving those gasses somewhere to expand before exiting the barrel OR by sopping up the heat and therefore energy of the exiting gasses either by an advanced baffling system or condensing the expanding heat on a thermally conductive surface such as steel wool etc.


As above, the captive piston design works very well for cartridge firearms, take a look at the PSS.

The heat and mechanical stresses on that thing are going to be large.


In terms of heat, I'm not too worried as it tends to dissipate fairly rapidly. Mechanically, a lightweight sabot travelling fast enough does have enough "oomph" behind it to cause serious damage so yes, a beefy unit is required. As you mentioned though, it doesn't compare to the catastrophic failure that would result if the projectile hits the barrel.

In this case, I'm fairly sure the foam keeps things centred, and I'm using multiple projectiles shotgun style, the hole is far bigger that it should be but this is for insurance purposes really, just in case the shot isn't centred.

Too big of a diameter however, and out comes the foam plug. Back to the drawing board...
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Unread postAuthor: Radiation » Wed Nov 26, 2008 3:13 pm

Ok I re-read what you wrote and I see where I got the idea it was an air gun, you wrote "air rifle" and I didn't really process that.

Any way on to my next point. From the article "Due to the nature of the round (tungsten shot), the practical lethal range was estimated at about 30 feet / 10 meters, which was sufficient for extremely cramped tunnels of Vietnam war. The sound signature of QSPR round fired from QSPR revolver was about 110 dB,"

I just wanted to point out, this gun is barely "silenced" 110 dB is very very loud. However a standard revolver type gun has a dB level of 120-140 which is significantly louder, but 110 db is about as loud as a car horn. :shock: It's actually loud enough to permanently damage your hearing.
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Unread postAuthor: jackssmirkingrevenge » Wed Nov 26, 2008 3:26 pm

Radiation wrote:I just wanted to point out, this gun is barely "silenced" 110 dB is very very loud. However a standard revlover type gun has a dB level of 120-140 which is significantly louder, but 110 db is about as loud as a car horn. :shock: It's actually loud enough to permanently damage your hearing.


Are you sure?

Have a look at these results.

The site, which is very reputable, quotes the sound of a 22LR shot unsuppressed as being in the region of 160 dB. A revolver would tend to be louder due to gas escaping between the cylinder and the barrel.

When fitted with various quality suppressors, the sound goes down to around 120 dB. Now, a suppressed 22LR is very quiet - folks shooting them certainly don't feel the need to wear ear protection - comparable to a low powered airgun, so the 110 dB figure quoted for the QSPR sounds very reasonable to me.
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Unread postAuthor: Radiation » Wed Nov 26, 2008 3:35 pm

I'm sorry, you're talking to a sound guy here. AV was my career for almost 10 years running. 110 dB is extraordinarily loud, cover your ears and wince loud. For a few seconds at 110 dB you're not going deaf (still potential for hearing loss here at 110-120 you should wear ear protection), but then again if the object is to keep your neighbors from calling the cops you are almost guaranteed to fail.

160 dB is what we call instantly deafening. 120 dB is as loud as a jet engine and is not what anyone should consider silenced, supressed yes, but simple supression does not appear to be your goal if I am not mistaken. You want silenced which by most defenitions I've seen means capable of being fired in closed quarters without obvious rapport or causing those around you specific alarm or recoginition that a gun was just fired based on the sound output. 110 dB would make almost anyone say "WTF was that loud bang?"
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Unread postAuthor: jackssmirkingrevenge » Wed Nov 26, 2008 3:53 pm

I would hardly call a suppressed 22LR pistol extraordinarily loud, in fact it is hardly noticeable. I can't fire one next to you to make the point, the closest I can offer is to tell you to have a look at such pistols being fired on youtube, not exactly deafening. Also take a look at the dB levels of various air rifles here, in the nineties range at point blank but very kind on the ears in practice.

I'm not doubting your credentials, but are you perhaps not making a difference between the brief sound blip of a shot and a constant tone?
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Unread postAuthor: Ragnarok » Wed Nov 26, 2008 3:56 pm

Radiation wrote:110 dB is extraordinarily loud, cover your ears and wince loud.

...If it's heard for a prolonged period.
Over the tiny fraction of a second of a gun shot, it doesn't sound that loud, because it doesn't last long enough. That is also the peak volume - you need to cut off about 30-40 dB for the perceived sound level when working with these very short pulses.

It's also measured at about 1 metre from the muzzle. Back off to 10 metres, and it's suddenly dropped to 90 dB peak, which if you consider the short pulse length sounds more like 50-60 dB, which is a lot less noticeable.

I know the peak volume level of my air rifle (at least, with the silencing insert removed) is greater than that of my launchers,as evidenced by my measurements, but my launchers sound a lot louder because the report lasts much longer, and consists of a greater air volume.
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Unread postAuthor: Radiation » Wed Nov 26, 2008 4:02 pm

You're right it probably isn't very loud. Outdoors. Sound propagates outside in a radial pattern away from the source which causes the over all sound to be a lot less. You appear to be shooting your gun indoors where walls, floors, and the structure itself will reinforce the 110 dB. Not suggesting you or anyone should do this, but firing that same suppressed 22LR pistol indoors in a neighborhood setting would yield a different result in the perceived loudness vs. being fired outdoors.

I don't know maybe if the sound was changed from a "BANG" to a "WOOSH" it would be less noticable. That is one of the goals of suppression/silencing, to change the sound so it is not recoginizable as a gun shot.
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Unread postAuthor: Ragnarok » Wed Nov 26, 2008 4:56 pm

Radiation wrote:Not suggesting you or anyone should do this, but firing that same suppressed 22LR pistol indoors.

I've been daft enough to fire my air rifle and dry fire HEAL while indoors...

The air rifle wasn't too bad, but HEAL practically took the curtains on the other side of the room 8 yards away off their runners, and nearly scared the life out of my family.

Behemoth wasn't quite so bad when it was fired indoors, but I was only using 3 bar, not 21 - and it did prove to my brother that his dodging skills were nowhere as good as he'd been claiming.
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Unread postAuthor: Radiation » Wed Nov 26, 2008 5:12 pm

Ragnarok wrote:Behemoth wasn't quite so bad when it was fired indoors, but I was only using 3 bar, not 21 - and it did prove to my brother that his dodging skills were nowhere as good as he'd been claiming.


:shock: :lol: :shock: :lol: :shock:
I hope it was a wadded up tissue paper you shot at him! :P
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Unread postAuthor: Ragnarok » Wed Nov 26, 2008 5:32 pm

About 100 bits of rolled up tissue paper each about the size of a paintball.
I don't think they can have been travelling any faster than about 30-40 m/s, a very leisurely speed in spudding to be honest (about 70-90 mph), and he still failed to dodge them.
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