How To Choose The Right Suppressor

A suppressor is designed for the caliber it’s meant to handle. Find out how to choose the right suppressor, especially if you want to use it on more than one gun.

Tips to choose the right suppressor:

• Understand Pressure Limitations For Your Caliber
• Not All Rimfires Are The Same
• Consider Suppressors That Can Be Used With Multiple Firearms
• Decide On A Mounting Method: Direct-Thread or Quick-Detach

Suppressors are designed for a specific use. That is, they are made to fit a particular caliber because bullet size, gas flow and pressure matter. I don’t care how good a 5.56 suppressor you own, if you put it onto a .308 rifle you are going to be very unhappy, very quickly. Try as it might, the bullet is not going to fit through the hole in the baffles and will end up making its own holes. Thus, the importance of choosing the right suppressor.

We’re jumping ahead a bit here, but rimfire cans, 5.56 cans and 9mm ones will have the same thread pitch; one-half-inch in diameter, with threads pitched at 28 per inch.

A rimfire suppressor screwed onto a 5.56 rifle will have a short and unhappy life, and it will be even shorter and messier if it is threaded onto a 9mm pistol. If at some point in the future you have any of these combinations in firearms and suppressors, be very, very careful what you put on where. And do not let your friends, relatives or gun club buddies at the range just screw on whatever suppressor fits. If you don’t attach the right suppressor, the results could be very bad, or at least, quite expensive.

Finding The Right Suppressor By Caliber

A suppressor is designed for a particular volume and strength, according to the caliber it is meant to deal with. As a result, you’ll see limitations from the manufacturer on a suppressor. “Rated for .308 Winchester, barrels longer than 12 inches” is one example. Or, “Rated for .300 RUM down to 16-inch barrel, .300 WinMag to 12 inches and .308 to 8-inch barrel lengths.”

They have designed and constructed a suppressor that can handle a certain amount of pressure and can deal with a certain maximum gas flow volume, and they are being up-front about what their suppressor will take.

Why? Simple, the noise you hear is caused by pressure. When the cartridge is fired, the chamber pressure is at its maximum, then the pressure goes down as the bullet moves forward, due to the increasing volume of the bore, with the bullet as the plug. When the bullet leaves, there is a certain pressure at the muzzle, called the “uncorking pressure,” and that is what causes the noise we are trying to control.

The higher the initial pressure, the greater the residual pressure down the bore. The shorter the barrel, the higher the uncorking pressure, simply because the expansion volume of the bore hasn’t increased enough to drop the pressure.

And here’s the important part for those of you interested in putting the right suppressor on your big boomers: the powder you use (or the ammo company uses) also makes a difference. A slow-burning or “progressive” powder acts to keep the bore pressure up as the bullet travels forward. That is part of how it gets you more velocity. (That, and a higher starting pressure.) So, your .300 magnum, of whatever type, is going to not only burn more powder, but a slower-burning powder than a .308 would, and this increases both the volume and uncorking pressure that a suppressor has to deal with.

That’s why suppressors are rated for a minimum barrel length.

As long as you are within the pressure and volume limits the manufacturer lists, and at or under bullet diameter, you are okay.

Your .308-rated suppressor will be just fine, and happy as a clam, if you put it onto your smaller-cartridge-case rifle or smaller-bullet-diameter rifle. That is, the 6.5 Creedmoor, 6.5 Grendel, .260 Remington, 243, etc. It will find a .223/5.56 rifle a piece of cake to deal with, being both a smaller case and smaller bullet.

However, it will not be as happy with a .270 Winchester or .280 Remington, and it will be very unhappy if you put it on a 7mm Remington Magnum.

You have to consider bullet diameter, chamber pressure, case volume and expected burn rate of common powders if you are going to use a suppressor across cartridges and in different firearms.

When in doubt, drop a line to the manufacturer. They’ll be happy to tell you if what you have in mind is okay or not, and if you have the right suppressor for the job. In fact, they’d prefer it if you ask ahead of time.

Rimfire Suppressor Considerations

Rimfires are not just rimfires. There is the common and expected (but surprisingly sharp) .22LR. The Twenty-Two Long Rifle has a chamber pressure of 21,000 PSI, but the expansion ratio (the ratio of the case compared to the case plus bore when the bullet leaves the muzzle) is so great that pressure has dropped to perhaps the firearm’s minimum by uncorking.

Change that to the .22 Magnum and things get more involved. Not because the expansion ratio is so much different, but that the magnum uses different powders and retains more pressure, garnering the extra velocity it is marketed for. Ditto the various .17s.

And then when you go to the 5.7×28, the FN cartridge, the case is a lot bigger, the expansion ratio is much smaller, and the uncorking pressure a lot more. As a result, some rimfire suppressors will be rated for the 5.7 and others will not.

As above, when in doubt, ask. Putting your perfectly fine and happy with your 10/22 rimfire suppressor on your buddy’s SBR’d FN PS90 may make for a bulged or broken suppressor.

Choosing The Best Suppressor For Handguns

The common handgun suppressor is for the 9mm, the most popular. There are others made for the .40 and .45, but they are less common. It is typical for someone who wants one suppressor to fit them all to buy a .45 and have rear cap adapters to fit it onto 9mm and .40 handguns. Yes, it has larger bore holes than would be called for in those applications, and thus will be a bit noisier, but it will amount to a decibel or a few at most. That, compared to the cost savings of having just one, appeals to many.

The Right Suppressor For A Rifle

Most people either get caliber-specific suppressors, or they invest in one or two (or more). The common approach here is to buy a .308 and use it on everything .308 and smaller, including 5.56, and add a second one that will handle the big magnums, like the .300s, or even jump up to a .338 suppressor, which will laugh at the efforts of your biggest .300 magnum.

How To Attach A Suppressor: Mounts

You can’t just use duct tape and baling wire to secure a suppressor. There are two types: direct-thread and quick-detach (QD). Some manufacturers have begun making suppressors with a rear cap that is a socket, and you can then thread into the socket either a direct-thread or a QD system.

Why elaborate systems to keep the suppressor on? Simple, each time you shoot, the jet of gases flow out of the muzzle, behind the bullet, and crash into the first baffle, the first surface ahead of them in the expansion chamber. “Big deal,” you say? Let’s do a quick bit of math. If the uncorking pressure of your rifle is only 7,500 PSI, and the impact surface of the baffle in the expansion chamber is only one-half of a square inch in surface, then the suppressor gets hit with a jet of gas that generates 3,750 pounds of impact. Impact that is trying to drive the suppressor off the muzzle.

That’s why you want good, sturdy threads on your barrel.

Pros And Cons Of A Direct-Thread Suppressor

This is exactly what it sounds like. An example would be a 5.56 rifle with the muzzle threaded for 1/2-28. The rear cap of the suppressor would be threaded 1/2-28, and you simply screw the suppressor on (after taking off the flash hider, if any) and tightening it to stay.

The advantages of direct-thread are obvious: It is less expensive, it is lighter and it is durable. The disadvantages are equally obvious: You have to spin your suppressor for as many turns as it takes to get it tight. If the thread pitch is 28 tpi, and you have half an inch of threaded shank, then it will be fourteen turns to tight.

Tight for a rifle suppressor is not just hand-tight. You will want to use a wrench to generate enough inch-pounds of torque to keep the suppressor on tight.

If you have one rifle and you won’t be using your suppressor on any other, then direct-thread is a no-brainer. If you are going to use it on more than one, then it is a decision between you and your wallet as to your choice.

The options are:

• Buy a suppressor for each rifle;
• Keep a wrench handy to swap suppressor or suppressors around on your rifles; or
• Buy a suppressor that uses a QD mount and install those mounts on each rifle so you can quickly swap the suppressor.

Quick-Detach Suppressor Mounts

This also, obviously, means quick-attach. The process is simple. The manufacturer makes a device that threads onto your barrel. This device has a set of threads or a quick-lock system that the suppressor latches onto. You can screw the suppressor onto the mount with a turn and a half. Or, slide it on and turn the locking collar a half-turn to lock on the suppressor.

The advantages are several. First, you can have a flash hider or muzzle brake on your rifle, even when the suppressor is off, if that’s how the mount is made (and many are).

You can swap your suppressor from one rifle (or handgun) to another quickly, without the use of tools. Of course, this supposes the suppressor is cool, as you won’t be swapping a suppressor bare-handed when it is at 700 degrees.

The big deal with this is economics. I just did the arithmetic with a suppressor that happens to be on my desk as I write this, a Sig SRD556QD. Sig makes the same suppressor as a direct thread, the SRD556.

The SRD556QD lists at $695 and mounts are $60 each. The SRD556 is $545. By the time you buy two SRD556 suppressors, you could have bought one SRD5566QD and six extra mounts. If you have that many .223/5.56 rifles, you can swap one suppressor between them.

The downsides are also simple: a QD-built suppressor is going to cost more than a plain direct-thread model. (That is, manufacturer-specific, model-alike.) Also, because of the mount and the rear of the suppressor that has to be machined for it, the QD model will be a bit heavier than the direct-thread version. In the case of the ones just used as a comparison, the SRD556 weighs 11.5 ounces and the SRD556QD weighs 14 ounces.

Editor’s Note: This article is an excerpt from The Suppressor Handbook by Patrick Sweeney.

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