Internal volume

[plooker]

Does increasing the volume of a suppressor help? Would a short(within reason) fat can be equal to a longer thin one with the same type and # of baffles? I'm wondering if it'd be posible to make a suppressor that is an oval/rectangular shape with the bulk of it below the sight line. It'd have to be a quick detach I think.

[mpallett]

I think the answer is yes AND no.

More volume is better. We have played with some .223 cans that were short and fat but the didn't seem to work as well as a longer thin(er) one.

There must be some ideal ratio for volume to length that deals with the impulse of the expanding gasses, etc.

Thoughts?

[William Perkins]

Does increasing the volume of a suppressor help? Would a short(within reason) fat can be equal to a longer thin one with the same type and # of baffles?

I have a 25 year old booklet (copyright 1982) that is 15 pages long from Dr. Dater called the "Art of Silence" in it he lists several "rules of thumb."
1. Internal volume should be 20 x the internal volume of the bore.
2. The entrance chamber should be 40% of the free volume of the suppressor.
3. Length should be 6 - 7 x the diameter.

I love these older materials. Virtually no one in the US was building suppressors back then except Dr. Dater and Jonathan Ciener. So all knowledge of the day was based on personal experience and technology that was 25 - 80 years old. Yet even with the acceleration of advancements in the field of suppressors in the last 10 - 15 years, these guidelines are still valid and used today.

This booklet (and others) are still available for sale today directly from Gemtech.

Children today are tyrants. They contradict their parents, gobble their food, and tyrannize their teachers.
Socrates, 5th century B.C.

[plooker]

Loved the quote, as it is and forever will be timeless.

[silencertalk]

So a 5.56mm can on a 14.5 inch barrel needs a volume of 11.4 ci. This means a can of 1.5 inches by 6.5 inches. Although 6 * 1.5 is 9.

If the barrel was 20 inches the volume of the can would need to be 15.8 ci. This means a can of 1.5 inches by 9 inches.

If anything I would have guessed the shorter barrel needed the larger can.

But anyway, this seems to imply that a 1.5x9 inch can would be good for a 5.56mm rifle. Well that sounds right.

Now a .50 BMG can for a 28 inch barrel would be 115 ci. That is a 3x16 inch can. Or maybe 2.75x20.

Most .50 BMG cans seems to be in the 2.25x12 inch range -- although they do not work very well.

So making a 3x16 one would be interesting.

[William Perkins]

If anything I would have guessed the shorter barrel needed the larger can.

Ya see what I mean then? Intuitively, one would think that the longer barrel would require a smaller suppressor, but the formula indicates otherwise. Well, guess what. Al Paulsons Volume 1 book on silencers offers anecdotal evidence that seems to agree with the formula. There is a chapter where he tests multiple .22 LR suppressors on a .22 pistol and a .22 rifle. The pistols NET better suppression than the rifles. Sooooooo it would seem that in order to NET the same degree of suppression, the rifle requires a LARGER suppressor to compensate, which coinsides with the theory of 20x bore volume. Interesting aye?

Most .50 BMG cans seems to be in the 2.25x12 inch range -- although they do not work very well.
So making a 3x16 one would be interesting.

Well this is probably a wee bit different.
1. .50 BMG has only recently been interesting to civilians (relatively speaking) which is the engine that drives the suppressor industry, so there was not any demand for .50 BMG suppressors in 1982. So the theory may not even apply. Have to ask Dr. Dater.
2. I think that the military is most interested in suppressing the Barrett M82. The US Army and the Marine Corps use the semi-auto Barrett (the Canadians use the much more accurate McBros. which dominates the civilian record books for accuracy records). Soundtech, AWC Sys. Tech. SWR, and Gemtech all offer suppressors for the Barrett. There is an upper weight limit of the suppressor before the weight of the suppressor makes the firearm unreliable. Reliability must be a higher priority over actual suppression. So the formula is secondary to reliability.

On another note I think it is interesting that the formula does NOT take into account the number of grains of powder in the cartridge. I treats a .22 short the same as a .220 Swift. For years, I thought this odd. Then I realized that size does not ALWAYS reflect performance. Size hits a point of diminishing returns. The discontinued Gemtech Hornet (larger) was not as quiet as the Gemtech Vortex-2 (smaller). That is the only example that I know of, of two different sized suppressors by the same manufacturer, that provided suppression numbers. But in general, larger seems to be quieter.

There is a period in the history of the individual, as of the race, when the hunters are the “best men,” as the Algonquin’s called them. We cannot but pity the boy who has never fired a gun; he is no more humane while his education has been sadly neglected.
Henry David Thoreau, Walden

[silencertalk]

The main reason there is more net reduction on a pistol is not necessarily because the can's work better on short barrels. The unsuppressed level is higher on pistol, so when you subract the suppressed level you get more net reduction. It does not mean that a suppressed pistol has a lower SPL than a suppressed rifle.

[Krink545]

This past weekend we had a little shoot/test. We shot a gemtech Predator on a 11" upper and a SWR Specwar1 on a 16" upper. We shot them side by side with the listeners about 20' behind us. We expected the 11" to be louder but the 11" w/ the Gemtech was quieter. When the cans cooled down we swaped them and reshot using the same shooters and liseners.
This time the SWR was quiter on the 11". Our guess was because of the lower velocity on the 11" upper. ??????

[silencertalk]

Or maybe the higher gas pressure helped the baffles work better. We shot a SoundTech can on a 7 inch upper and were very impressed.

[William Perkins]

The main reason there is more net reduction on a pistol is not necessarily because the can's work better on short barrels.

Well now that depends on your definition of work. On an unsuppressed 5 1/2" barreled Ruger MK II the SPL will be ~152dB, "A" weighted of course . On a 20" Ruger 77/22 the SPL would be ~ 139 dB. The unsuppressed rifle is 13 dB quieter than the pistol. If the suppressed pistol shows greater NET reduction than the suppressed rifle, I would argue that more "work" HAS been done. The fact that the suppressed SPL is higher does not negate that fact, since the baseline included a 13 dB handicap. The definition of work that best fits from Websters is "11. Mechanical. transference of force from one body or system to another" Greater NET reduction on pistols can be explained as a more effective transfer of force (work). More energy is stripped from the combustion gasses as a result of higher pressures in the shorter barrels.

The unsuppressed level is higher on pistol, so when you subract the suppressed level you get more net reduction. It does not mean that a suppressed pistol has a lower SPL than a suppressed rifle.

Completely agree. But, absolute SPL are NOT the numbers commonly printed by Al Paulson, Matt Smith, manufacturers, you or anyone else. This is entirely due to variances in day to day readings so it is unfair to use these 'soft' numbers. Net reduction, on the other hand is more of a 'hard' number, it is more consistant, therefore reproducable. So the only numbers consumers can compare is net. Many consumers don't understand the "net" can be higher on a pistol, but it will be louder than when the "net" is lower when mounted on a rifle.

A man who enjoys responsibility usually gets it. A man who merely likes exercising authority usually loses it.
Malcolm S. Forbes