This ones totally hypothetical. I was just wondering how a can would perform on a 20" barrel. You don't see em' alot so I was curious.

I don't have exact figures on this but it should work about the same as on a shorter barrel. Since the bullet will still be traveling faster then the speed of sound it won't truly be silent.

Edited to add: The quality of the suppressor will make the biggest difference.

It has been a while since I have had a technical discussion with those-in-the-know about suppressors but I will try to help (and I am subject to flaming correction from others...)

Suppressors 'work' just as well on one barrel length as any other generally.

The best way to understand suppressors is to consider them as having a fixed 'capacity' to reduce sound 'volume'. Say a given can has a suppression 'capacity' of 20 db. If you put it on a weapon that has an open sound signature of 140db, with the can installed it will have a signature of 120 db. A weapon with a 120db open signature will have a 100db signature suppressed with the sample can.

Now, that doesn't sound like much suppression...only 20db difference...but the decibel scale is a logrithmic scale where 2 is twice as 'high' as 1, 3 is twice as much as 2...140 is twice as much as 139, etc... ,so that 20db difference is significant.

Suppressors also change the 'character' of sound by stretching the pressure (sound) pulse of the muzzle blast over a longer period of time. Imagine the difference between the 'snap' of a snare drum in a highschool band and the 'thump' of a bass drum. They can be equally loud, but their 'character' is different.

With a suppressor, you not only achieve a reduction in the intensity of the pressure pulse (muzzle blast) when the projectile uncorks the barrel, but that pulse just doesn't sound like a weapon being fired! Plus, at a distance of not many yards, a suppressed weapon is more felt that heard...just like that bass drum...which can be confusing as to the direction the 'sound' came from.

I know that is a long way to give an opinion that barrel length doesn't matter how well a suppressor technically 'performs' because the suppressor does what it does regardless.

Ok, that makes sense. Thanks for the info. Now I wonder if I can scrounge up a thousand bucks to test it out for myself.[:d]

"<...> 140 is twice as much as 139 <...>"

no, that's not how it works.  every 3dB increase is a doubling of sound pressure level.  get your engineering books back out.

ar-jedi

Not quite... Every 3dB doubles the sound previous, but not the base reference or log -- as a logarithmic scale, 10dB is 10 times louder than the reference and 60dB is one million times louder than the reference.

It is true that a sound increase of 3 dB is twice as loud as the previous sound (P1)... but 6dB is not 4 times louder than P1 -- just don't work that way.

Ahhh...some things are too easy to predict...

I admitted it had been a while...and although the general trend of a small variation in db equals a large difference in sound pressure  level...I stand corrected, to include a snide, petty remark.

Priceless

Has their ever been research done on using
anti sound electronics to suppress firearms
signatures?

I thought about using active noise cancellation (ANC) for a suppressor, but I really don't think it would work.  ANC is really best at killing repetitive, periodic, low frequency sound.  Also, it is based on the interference of sound waves, so it is very directional.  You would have to emit (different) cancelling waves in all directions.  Power would be an issue, too.  Trying to generate a sound wave equal in magnitude to a gunshot with any kind of normal speakers would be a real challenge, I imagine.

The loudest part of a 5.56mm weapon firing is the sonic crack of the bullet with a can mounted.  A 20" rifle will have the same db level as a 14.5" barrel because the blast level will be below the sonic crack.  The report of the weapon before the can was attached will not matter if the suppressor was propperly designed.

They will have equal decibel reports.

ANC would be pointless.  The blast is lower than the sonic crack already and current technology is simpler, lighter and more durable.

Hummmm... This is really much more complex than what is seen at first blush. The practice of noise reduction must address the needs of the operator first - IMHO.

There are essentially three areas of cencern for noise level reduction: One is masking or hiding the report of the shot at the target (or areas in front of the weapon). For most readers of this board, this would never be a concern and deserves no further discussion.

The two other locations are to the side of the shooter (noise polution) and at the shooter's ear -- When we speak of these "areas", these are physical locations, the difference between the perceived noise level can be very different at each location.

Attenuation of side noise is nice and a concern for military and law enforcement operators -- The exposure to these noise levels by those "on line" is a major concern, as well is the possible reflection of noise back to the operator -- But, as I assume that most are interested in a suppressor for the safety and comfort of the shooter (and the cool factor)... I would offer the following.

First... all bullets have flight noise, does not matter if the round is so slow you can see it or if it is going 4000fps -- all bullets have flight noise. True, subsonic speeds produce noise levels that are so minimal that they are of no concern for this discussion, but when a round becomes transsonic, the flight noise increases greatly... to a point around 1300fps, where the report levels off for supersonic (above transsonic) and even hypersonic flight.

So, what does that mean? To the shooter, very little -- Bullet flight noise is a radial emission and with the exception of ground reflection and reflection from objects in front of and to the side, the shooter will perceive very little of the bullet flight noise. To anyone standing to the side of the bullet path, it will be much louder -- But even this gets a little tricky, especially from a hearing preservation stand point.

Just say that Joe's rifle has a muzzle report of 160dB -- the perceived report is actually the combination of 3 different sounds over a very short time... The bullet noise (or "crack"), the muzzle signature and ground reflection. All this is scrunched into about 30mS.

If we attenuate the muzzle report to below 140dB, the bullet noise will indeed be the loudest part of the new report, keeping the actual dB level at about 140dB. But, to the observer, it will "sound" even quieter, if the new levels are taken using a weighted scale dB(A), the difference can be seen... also, the duration of the new signature (above a painful level)will be much shorter (less than a few mS) making it seem "quieter" again. The best way to actually track the signature is to record and graph it, peak dB levels can not show nearly as much as time graphed frequency and kilopascal levels.

The safety concern is that the observer is still being subjected to damaging noise levels, but is beeing "fooled" that they are not as bad as they really are -- This is compounded in real life by the observer "beleiveing" the signature is not as loud, because they know it has been suppressed.

Crap... I am rambling, cutting to the chase: If you want to screw a can on your centerfire, high-velocity rifle, it will still be loud. To the shooter, it will most likely be a "have to raise your voice to get over it loud", but some say that the suppressor can replace hearing protection for the shooter... maybe not. It is a viable solution for reducing the level to below a sudden and permanent damaging level.

If you expect that really quiet, mouse pissing on cotton "phitt" sound, you need a system that matches the weapon, ammuniton and suppressor for that effect -- and there are trade offs, naturally.

This system will produce the mouse pissing on cotton sound you speak of.  It's actually (to the ear) quieter to shoot than to dry fire, because the PING of an empty chamber seems much louder.[img]http://sniper.rsvs.net/7722Right.JPG[/img]

Like I said, a system built for that purpose can be very quiet... I have shot rifles that made no more noise than the action tightening (sounds like ice cracking when you first put it in a glass)!

That has been my observation with several cans. That crack can be pretty damn loud, almost to the point of needing hearing protection.

Nice looking rig, QS.  What caliber/can is that?

It's a Ruger 77/22 stainless .22LR with an AWC Archangel III muzzle can.  I took the tape off the can for illustrative purposes.  It shoots cloverleafs all day at 50 yards with Eley Subsonic Xtra Plus or RWS subsonic.

AWC did all the work on it - shorten, crown and thread the barrel, and trigger job.