by Steve Adelmann - Tuesday, October 26, 2010
Hollywood has long depicted barely audible suppressed firearms, closer in sound and accuracy to sci-fi lasers than a tool fired by primer and powder. Veteran sound suppressor users know that's not quite the way it works; "cans" can be noisy, temperamental and some aren't worth their weight in scrap. Yet when properly designed, manufactured, understood, trained with and maintained, suppressors are supremely useful tools. Yes, that's a mouthful of caveats and it requires actual work; most good things do.
Militarily, sound suppressors are used to lower the signatures of shooters or combat operations and sometimes even conceal the very presence of forces. To achieve this, they reduce any combination of audible sound, muzzle flash and blast disturbances to ground surfaces. In practical terms, suppressors are generally employed in one of two ways: either as full-time flash-and-sound suppressors for normal munitions, or as tools of stealth, intended to hide the origin or occurrence of a precise shot. Though the purposes are similar, they require different equipment and training.
Much sound suppressor technical material is available, none of which I can replicate here. A good example is "Silencer: History and Performance, Volume 1" by Alan C. Paulson. This primer contains easy-to-understand technical information and historical analysis. Rather than attempt that route here, I'll focus on observations and lessons learned from a military career filled with testing and employing sound suppressors on pistols, submachine guns, carbines and sniper rifles.
The Accuracy Connection
The principal suppressor attachment methods are integral, thread-on and quick detachable (QD). In terms of sound reduction, integral suppressors—built as part of the gun and/or barrel and intended for full-time use—are the most efficient. Unfortunately they also have practical limits when used in dynamic environments. Integrals very often require a complete barrel change when damaged or worn out and the extra weight, length and bulk remain constant. Of the remaining methods, thread-ons tend to exhibit less zero shift between unsuppressed and suppressed zeros. How-ever they lack positive indexing, so differences in tightness and points of impact (POI) can occur with each mounting. Their threads also tend to trap carbon, causing suppressors to get stuck after heavy firing. An anti-seize compound applied to the threads helps. None of this means thread-on suppressors are undesirable. J.D. Jones, of SSK Industries, makes several very high-quality models that are used successfully in capacities ranging from animal control to precision-fire tactical rifles.
QDs have the current edge over thread-ons in convenience and consistency, but can be quirky and finicky performers. They've been known to induce hair-pulling frustration on accuracy aficionados, and I have the bald head to prove it's true. One reason is the mount has to have enough bearing surface to allow the suppressor to be as "true" to the bore as possible. That requires a balance between keeping mount size and weight low, while preserving strength and consistency from one mounting to another. Another QD challenge is designing an attachment system durable enough to withstand high heat and abuse, yet easy for troops to remove in all conditions—cold, wet, dark, etc. It's not impossible, but to be truthful, many of the QD suppressors on the market are merely expensive muzzle brakes. Nonetheless, there are a few good apples from progressive companies like SureFire, which is striving to meet the tactical market's needs with well-designed, functional suppressors. As a testament to its position in the industry, SureFire tactical suppressors are either currently fielded or being procured by USMC Scout Snipers, Air Force Reserve Para-Rescue Jumpers and several independent Army units.
Assuming the rifle, optic, shooter and munitions are all doing their parts, a good suppressor and mount will limit point-of-impact shift from unsuppressed to suppressed. This is most important on a firearm intended to be used in both configurations. While some shift is likely due to harmonic changes to the barrel, the closer suppressed groups are to the unsuppressed point of impact, the better. Horizontal shift is the toughest to accommodate, particularly when combined with vertical shift. How much is acceptable? That's dictated entirely by how it will be used and who's doing the shooting. Civilians have a lot less at stake than military or LE shooters, so tolerance is relative to need and individual capability. In addition to causing zero shift, suppressors can affect velocity. Some pistol-caliber integral suppressors are designed to scrub velocity off supersonic ammunition to achieve subsonic speeds. In other cases, suppressor design actually gives a slight boost to muzzle velocity, also changing the vertical point of impact.
Look for suppressors that have minimal, point-of-impact shift from one mounting to another. Also note changes for different ammunition types. If you have access to an armory with multiple suppressors for issue, draw several and shoot all to determine which is closest to your unsuppressed point of impact. Ensure flash suppressor/muzzle brake mounting instructions are followed closely. Don't forget to make sure group size doesn't open with the sound suppressor in place. If it does, there's likely either a problem with the mount or projectiles are dragging somewhere in the suppressor. It's important to understand that two like guns of the same configuration will likely have different results with the same suppressor. This is no different than the same cartridge load flying differently out of two like barrels. Don't be fooled by the performance someone else has with a specific suppressor on a gun similar to yours. Individual rifle ballistics are like fingerprints: No two are exactly the same. Embracing this idea before comparing notes is a great way to avoid frustration.
When attaching a QD suppressor, do your level best to ensure its locking mechanism is tight and in the same position each time. The tremendous gas pressure is enough to blow an improperly attached suppressor off the mount, creating a potential for serious injury and equipment damage. If it has a rotating ring with a spring-loaded lock, such as SureFire's, it's recommended the lock ring be tightened as much as possible by hand. A common mistake is to try to count clicks on the ring's teeth instead of just getting it as tight as possible. You'll find that tightening properly will lead you to a natural index point, helping repeatability. For other QD systems, such as those locking on gas blocks, ensure they're fully seated and locked in place. A tight suppressor is a happy suppressor.
The Sound of Silence
While BATFE classifies them as "silencers," sound suppressors are anything but silent. They're expected to reduce some degree of overall sound pressure level (SPL), most often expressed in a decibel measurement. Here are a few points worth knowing when evaluating suppressor sound reduction.
How you hear a report when shooting may not correlate with measured sound reduction. The quietest measured suppressor may be louder to your ear because of differences in how we hear, versus what's measured by a sound meter. If you line up 10 people and have them rate several suppressors, they'll come up with different rankings.
We see decibel ratings listed, but these numbers mean nothing without knowing details like microphone position in relation to guns. A sensor may be positioned to capture SPL behind the gun, at the action/ejection port, muzzle, downrange or in combination, all resulting in different numbers. That information is best used for comparisons against similar measurements of other suppressors with the same gun, ammo, conditions, etc.
Simply having a suppressor on the end of your gun doesn't mean it's quiet enough to conceal a shot. When shooting supersonic ammunition, suppressors only reduce muzzle report while doing nothing for the bullet's sonic "crack" as it moves downrange. Anyone along that flight path will hear the projectile pass loudly, and anyone to your rear will hear a slightly muted shot. Even subsonic projectiles aren't silent. While there's no crack, they zip downrange with an unnerving sound when heard from the receiving end. The larger the projectile, the more noise it makes disturbing the air in flight. This applies to both supersonic and subsonic projectiles, though it's a different sound for each. Likewise, larger-diameter suppressor bores generally equal more noise at the muzzle. The smaller the bullet and tighter the bore, the less noise escaping, all else being equal.
Before deciding which suppressor to bet your life on, learn how it performs in all areas. When you compare decibel measurements from different sources, do so with no more confidence than you'd have of a politician keeping their word. Sound meters suitable for measuring firearm SPLs are expensive and hard to find. Since most of us can't afford to hire an independent test lab, we're left with our ears, published figures and the scant independent studies made available to the public. Unfortunately many available figures result from sound meters designed for OSHA-type workplace measurements, which mischaracterize noise impulses from firearms. Beware the snake-oil salesmen on this point, the suppressor world is full of them and the game they're dealing has lethal implications for professionals. One practical test I've used is placing people in ballistically shielded positions, evaluating different suppressors by ear from varying distances and directions. There are many subjective variables in this test but it can be enlightening when counterweighed with SPL measurements or as part of a side-by-side comparison.
As with bores and chambers, heat is an enemy of suppressors and mounts. I mentioned in "We Own the Night," in the January issue, that some flash suppressors and muzzle brakes will melt during heavy shooting events. Although it takes several hundred rapidly fired rounds to cause this, it's worth noting that the best designs don't melt down so easily. More commonly, minute cracks appear around the flash suppressor's cut outs after heavy firing. The sound suppressors themselves suffer similarly. Just like barrels, more rounds fired equal less suppressor life. Design and material have a lot to do with expected life, but even the most advanced metallurgy and engineering can't provide immortality. In many cases, when a suppressor is "shot out" it will cease to provide much sound suppression. Warped baffles and other parts close to the line of bore may be nicked by projectiles, destroying accuracy and creating a potential hazard.
While it may be impossible to restrict firing in a real fight, in training it's wise to limit rapid-fire suppressor events. It's always important to verify function since a system's timing and operating pressures may be altered. Also check effects on accuracy with any likely ammunition types. Limit training sessions to a few magazines, without overheating the gun and suppressor in the process. As a rule of thumb, if you're baking off the can's finish, it's time to let everything cool down. If it's glowing red, call it a day and, once cool, inspect the suppressor before using it again. Keep a rough record of round count, just like snipers do with match barrels. Eventually you'll get an idea of how long a given type of suppressor will last.
The very effective, baffle-style muzzle brakes seen on large-caliber guns are carbon traps. When using supersonic ammunition, sound suppressors are worse, akin to carbon sinkholes. By design, gasses following a projectile out of the bore are routed into the sound suppressor. Unfortunately, carbon and unburned powder come along for the ride. While much of it burns away, enough is left that QD suppressors can be difficult to remove. If left in place too long without cleaning, the muzzle mount and suppressor may rust. In extreme cases of neglect, corrosion will wind up fusing the two, resulting in an unintentional integral suppressor and more work for your gunsmith.
If possible, use loads tailored to your barrel length for efficient powder burn. Most tactical users often have little flexibility here, being issued ammunition without much choice. Ensure prior to attaching the QD suppressor that all mounting surfaces are clean and free of carbon, debris and rust. A light coating of high-temperature grease won't hurt as long as you don't lay it on so thick it interferes with proper mounting. Cleaning after a shooting session is highly recommended, and removing the suppressor will reduce chances of it sticking. Refer to the manufacturer's cleaning protocol, as it varies with type. All-metal suppressors with steel, titanium or Inconel baffles generally allow the use of cleaning solvents, but suppressors with replaceable, synthetic wipes don't.
There are some suppressors that can be disassembled for cleaning and others are welded shut. Ensure that the medium used for cleaning is completely removed before firing the gun. A high-pressure air compressor helps blow solvents out; just ensure the you wear proper protective gear. Flash suppressors and muzzle brakes can likewise be cleaned with bore or carbon solvents and brushes. If you wait too long to clean the mounting surface, more than likely you'll need a scraper and some spare time.
Miscellaneous IssuesWet vs. Dry
Many of today's suppressors are designed to provide maximum SPL reduction when "wet." This generally means the baffled area is filled with a sound-dampening medium, like water or grease. Caution: Always follow the manufacturer's instructions for wetting a suppressor. While they definitely provide a noticeable sound reduction, extra care and preparation is required. Don't run out and try filling your suppressor with anything. These devices create a tremendous amount of back-pressure when dry; if you make a mistake and obstruct the bore the result can be fatal. Follow the manufacturer's instructions and always wear eye and ear protection when shooting.
Subsonic Ammunition Performance in Rifles
The use of subsonic rifle ammunition in concert with a sound suppressor is a technical and voluminous subject. It's commonly used to conceal the location, if not the very act of firing. Subsonic ammunition velocities can vary wildly as an action, barrel and suppressor heat up. Challenges in filling excess case volume (due to less powder needed for subsonic velocities) also add to trajectory variations. Subsonic projectiles behave differently when supersonic. Different bullet designs work best in each velocity range, and subsonic terminal performance can suffer when expanding projectiles are used. Since high velocity is normally a critical component to expansion, subsonic rounds often over-penetrate soft tissue, regardless of design. Subsonic precision work is similar to long-range shooting (beyond 1,000 meters): Small errors that normally incur minor deviations in normal shooting are magnified exponentially at subsonic velocities. The techniques to manage these variations are an article unto themselves. Suffice it to say that competent snipers develop a specific protocol for precision subsonic fire, knowing the exact limits of range and effectiveness. If you intend to shoot subsonic rounds, plan to shoot as many as possible in training to learn the ins and outs.
Unfortunately the National Firearms Act of 1934 resulted in unnecessarily heavy regulation (and political vilification) of sound suppressors on this side of the Atlantic. I don't normally espouse European societal norms, but this is an area where many foreign countries have it right. In the old country, suppressors are relatively inexpensive, commonplace and often required for public shooting and hunting. While they're still legal to own in the United States, additional fees and registration steps are required for legal transfer. Nonetheless, sound suppressors are a great accoutrement for many firearm types, helping to reduce hearing impairment and noise complaints. For our troops fighting abroad, suppressors are lifesavers; helping to conceal their locations when taking the fight to the enemy. With adequate training time and maintenance, a high-quality sound suppressor will reward you with many years of quiet service on range and field alike.
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