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Suppressing pistols: getting the most out of your threaded barrels
Guns & Ammo. 60.3 (Mar. 2016): p58+.
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PISTOLS WITH THREADED BARRELS are seeing a parallel surge in popularity as gun owners become educated on the facts about suppressor ownership. Years ago it was work to get a threaded pistol barrel. Today, there is a growing acceptance of sound suppressors (aka "silencers") among the mainstream, which is a good thing.

The most recent introduction of pistols with factory installed threaded barrels comes from Springfield Armory. It has unveiled the XD[M] series chambered in 9mm and .45, each with an extended and threaded barrel. Don't have a suppressor or waiting on ATF approval? Both pistols come standard with screw-on thread protector ring. If you're a G&A faithful, the XD[M] is already familiar to you, so we won't go into a lengthy recitation of its features, but rather outline how the new ones differ.

To provide clearance for the suppressor mount, the barrels need to be extended in length and threaded. The full-size threaded barrel variant utilizes a 5.28-inch barrel compared to the 4 1/2-inch tube on the standard XD[M] of this size.

I spoked to Dave Williams at Springfield Armory who said, "We've been doing this in the Custom Shop for some time now. So many people asked for it [we decided to add] it to the lineup."

Interestingly enough, Springfield Armory has color coded the pistols. The 9mm Threaded Barrel model is available FDE, while the .45 is available in any color--as long as it's black.

Finally, there is the matter of aiming. If you use standard-height sights, the circumference of the average suppressor will interfere with your attempt at a sight picture. (This is dependent on the diameter of the suppressor used.) For this reason, Springfield Armory installs suppressor-height sights that can be seen over the tube of most suppressors.

The Booster One consideration to make when attaching a suppressor to a pistol is this: If the total mass of the moving parts (slide assembly including barrel) is too much, the system stalls and the pistol malfunctions. Some suppressor manufacturers deal with this problem by using a Nielsen Device, or Linear Inertial Decoupler (LID). It stores energy by means of a stout spring in the mount early in the recoil cycle. It then transfers the energy back into the system, driving the pistol. It essentially acts as a recoil booster. Certain pistol designs are more sensitive to extra mass than others, but all locked-breech pistols benefit from the boost a Nielsen Device provides.

Then there is the matter of the threads themselves. We can't just spin a threading die onto an extended barrel and expect things to work out well. Threads must be centered, aligned to the bore axis and straight, or you risk baffle strikes. Springfield Armory takes care of this while the barrels are being manufactured, threading them as part of the CNC lathe operation that turns the barrel out to spec.

"We didn't have to make any mechanical changes to the XD[M] to make it function reliably with a suppressor," Williams said. "As long as you use a booster, you're good to go."

How a LID works. As Einstein once remarked, "Physics is easy, life is hard." The physics of a LID are easy to describe, but not always easy to tune. Simply put, the suppressor tube and baffles ride on a cylindrical sleeve. The sleeve attaches to the barrel, and the two (tube and mount/sleeve) are connected by a spring. When you fire the pistol, its recoil and movement begins the moment the bullet moves. The pistol recoils back, but the suppressor, sliding on the sleeve, stays put. This compresses the spring, creating stored potential energy.

Once the recoil energy has been used up driving the pistol, the spring snaps back and brings the mass of the suppressor with it, delivering the stored energy back into the system. This movement further drives the recoil stroke of the pistol. Here's the curious thing; a suppressed pistol, with a LID, can actually feel as if it is recoiling "harder" than when unsuppressed. The total energy is the same either way, but you feel the recoil as two slaps, the initial setback and the energy delivery of the LID.

You can tune it with various springs, but the more you make it feel like normal recoil, the less operating margin you have and thus risk malfunctions.

The fit of the silencer on the mount must have some play, or else it would be too tight. The friction would prevent the LID from working. The alignment notches on the LID keep the tube oriented in a given axial setting. The unavoidable tolerances in the LID allows the silencer to vibrate, and where it sits on the LID affects vibrations. By adjusting the LID/tube setting from one notch to the next, you can change the harmonics of the vibration and the point of impact.

So, that's what you do. Establish a zero with the barrel bare, and then adjust the tube-on-LID setting, by way of the notches, until it is also zeroed. The process is simple; hold the unloaded pistol normally. Grab the tube with your other hand, and pull the tube forward. When you feel it slip off the notch, turn slowly until you feel the next notch, and then ease the tube back into place. Shoot a group with that setting, and compare. Continue until you have the suppressed and un-suppressed zeroes in agreement.

Every model, and particular pistol-suppressor combo is unique. If you change the suppressor to another pistol, it may need a new setting. If you change loads in the original pistol, it may need a change.

Going Quiet Now, the giggle-worthy part: The can. In addition to adding mass to the barrel, a suppressor also changes the harmonics of the barrel and the timing of the unlocking process. The big question people ask us, Does this affect accuracy? There's only one way to find out how a suppressor influences downrange performance. To that end, I delved into my silencer locker and hauled out a set of appropriate suppressors to evaluate Springfield Armory's new XD[M] pistols with threaded barrels.

For the 9mm, I first utilized a Gemtech MultiMount and a Gemtech GM9.1 also packed a Thompson Machine Poseidon 9mm and its cleverly named ISIS-2. These represent a good spectrum of design approaches, as the Gemtech MultiMount is an assembled baffle-stack design, while the other three are monocore designs. As an added variable, the Poseidon is compact, lightweight and does not require a booster. This is known as a wet can, as it uses a wipe coupled with a compact monocore. Traditionally, suppressors using wipes are of older technology, inhibit accuracy and need frequent replacement; I had to see what the effect actually is on this one.

In .45, I took a pair of suppressors to test: The Innovative Arms Shepherd, and a Gemtech GM45. The Shepherd is a classic assembled baffle-stack design, while the GM45 is Gemtech's latest monocore. Each incorporates a booster built into the mount.

Specialized Ammo? To test for accuracy shift, I needed ammo. In the interest of maximizing fun with the suppressors, I wanted the subsonic type. Keeping the task as consistent as possible, I placed an order for a sufficient supply of FIPR's loads in each caliber. Finding subsonic .45 ammunition is not a problem, as it is almost all subsonic except for the most energetic, lightest-bullet loads. HPR sent a 230-grain match offering for .45. In 9mm, I had to provide specifics with regard to bullet weight in order to get subsonic ammo. Pretty much only 147 grainers will do. HPR has the EMCON line featuring 147-grain 9mm specifically loaded as a subsonic for suppressor use. Since the Thompson Machine Poseidon uses a wipe, I wasn't too hot on hollowpoints, so I ordered the EMCON loaded with HPR's version of a full-metal-jacket (FMJ) bullet, the Total Metal Jacket (TMJ).

Expecting the Unexpected The process was simple; I testfired each of the XD[M] pistols, sans a suppressor, using a Sinclair rest at 25 yards to determine the point of impact (POI) and average group size. Then, I unscrewed the thread protector, installed a suppressor, and proceeded to shoot five, five-shot groups using the exact same setup. This took a bit of time, to first establish the LID setting that would get the suppressed zero in agreement with the un-sup pressed zero. Once I had them as close in agreement as possible, I recorded group sizes and POI of the group's center.

I expected that there would be some shift in both direction and group size. What I found was that the groups were, in many instances, smaller with a suppressor installed than they were without. This is common with rifles, as the suppressor acts to strip the muzzle blast away from the bullet just at the time in its flight when it is most sensitive to disruption. Also, any shift in group center was difficult, if not impossible, to sort out. An accurate pistol, and both of these are, helps. But, if you are shooting groups at 25 yards that are 2 inches or less, you'll still have a zero shift of at least 2 inches. Anything smaller and the variance in group center can be caused by the shooter, not the suppressor.

After getting the booster-equipped suppressors set on their correct notch, I shot for record. The XD[M] in .45 did not shoot groups as small as the 9mm, in part because the booster really makes it work. While the recoil increase in 9mm is noticeable, the increase in a .45 becomes a hindrance to accurate shooting.

If you do not hand-tighten a suppressor on properly and it vibrates loose, accuracy will immediately change. I had this happen once with the .45 and the groups went from 2 inches and centered on the target, to three shots spread across 8 inches, 6 inches from the aiming point. It's good to keep reminding yourself to check and make certain that the suppressor remains tight.

Lastly, there was a slight but consistent increase in velocity with the suppressor mounted. This is due to the residual pressure behind the bullet still giving a tiny boost in velocity. An interesting detail comes with the Poseidon. Since it is shorter, and has a wipe at the front cap, it cannot give as much velocity increase as the longer tubes. And the wipe probably negates any increase, as the Poseidon did not show the velocity bump that the others did.

What is a Monocore? Traditionally, silencers were created by stacking lathe-turned baffles inside of a tube and closing the ends. This can work quite well, but it does involve some compromises. A stack of identical baffles is easy to re-assemble, but may not be the quietest design possible. Making the baffle stack more efficient involves offsetting the turbulence, and that means a specific baffle assembly order. If assembled incorrectly, the silencer is less-quiet, or in some instances, can't be fit back together.

A monocore is a single piece of metal (in pistols, usually aluminum) that is machined on five-axis CNC machines. It slides into the suppressor tube, creating the baffle stack. The single chunk of metal allows designers to create more complicated baffle shapes, which can be more effective. Also, as a single piece, it is easier to clean and it is a snap to reassemble.

The problem for the manufacturer is that a monocore requires an investment in a five-axis CNC machining station, and an operator, while K or M baffles (the traditional baffle designs) can be made on a relatively cheap automatic lathe.

Does it need to be cleaned? You must get into the habit of cleaning your pistol suppressor. Where rifle suppressors run hot enough (and rifle calibers bum clean enough), a rifle suppressor is essentially self-cleaning. Pistol cans are not. If you do not strip and scrub your pistol suppressor (at least once each 500 rounds) you will find it carbon-welded. This is a condition where there is so much carbon buildup one can't wrench the suppressor apart without great effort.

Once apart, clean it with the same pistol-cleaning solvents and methods you've already been using. Dry-brushing it won't be enough, you'll soon carbon-weld your suppressor into one piece. Use solvents that are safe for aluminum, as most pistol-caliber suppressors are made of aluminum. If you neglect or forget your cleaning schedule, and you can't get your suppressor apart, life can be difficult. As neglect continues, a suppressor gets heavier and heavier as the carbon builds up, and it becomes less-quiet. If you get desperate and try to force it, you risk damaging the tube. If you have a suppressor that is carbon-welded, I suggest that you submerge it in Kroil for a few weeks. A longer time is better.

Will groups shift? Anything you put on a barrel can change accuracy. A pistol-caliber suppressor is a lot of mass to add to a muzzle. Manufacturers know this and work diligently to minimize changes. In this test, the changes were so small that it wasn't really clear if any had happened. To further explore this subject, we'll have to use a machine rest. While that seems simple, it may not tell us what we want to know. Handling a handgun while it is in the rest changes accuracy and zero until it is fired enough to "settle it into" the rest once more.

What is a wipe? Early in suppressor technology, many considered wipes or rubber disks best to seal the gases in. The trouble was, with a multi-inch stack of rubber for the bullet to squirm through, accuracy often suffered. So, they fell out of favor. There's no free lunch. Wipes wear and gradually get noisier until they are swapped out. And an old-school wet suppressor is a splatter-can. They spray black, oily residue on everything within a few feet. If you want to run your can wet--and some are not meant to be --that's between you and your laundry service.



                        (FPS)                   (IN.)        GROUP

None                     951      12     5       1.25         1.75
Thomp. Mach. ISIS-2      960      21     9        1           1.5
Poseidon                 948      35    14       1.25          2
Gemtech GM9              968      16     6       .875         1.45
Gemtech Multi-Mount      969      32    12        1           1.6

Notes: Accuracy results are averages of five, 5-shot groups at 25
yards off a Sinclair front shooting rest. Velocities are averages of
10 shots measured on a Labradar chronograph set to record 15 feet
from the muzzle.


                   (FPS)                   (IN.)       GROUP

None                845      48    20       2.5         1.75
I.A. Shepherd       873      85    35       2.5          2
Gemtech GM45        871      71    29       2.25        1.75

Notes: Accuracy results are averages of five, 5-shot groups at 25
yards off a Sinclair front shooting rest. Velocities are averages of
10 shots measured on a Labradar chro-nograph set to record 15 feet
from the muzzle.
Source Citation   (MLA 8th Edition)
Sweeney, Patrick. "Suppressing pistols: getting the most out of your threaded barrels." Guns & Ammo, Mar. 2016, p. 58+. General OneFile, Accessed 21 Nov. 2018.

Gale Document Number: GALE|A443283901