What is a suppressor?
Not a legal definition, but more of a practical one:
A suppressor is a device that decreases the signature of the firearm. The signature can be of different types.
Classically we think of sound, however, flash is a significant source of signature.
A third one that I am now considering as relevant is IR/heat signature.
There are different types of suppressors, but most of them work in the same principle for sound reduction. The gas coming out of the end of the barrel expands very rapidly causing a pop. By slowing the gasses and preventing it all from expanding at the same moment decreases the pop. This is analogous to opening a champagne bottle, cork very slowly. In addition, a small amount of signature reduction is by cooling the gasses.
Factors to consider when evaluating a suppressor:
The natural inclination for evaluating a suppressor is to judge it based on sound volume reduction. I would advise that there are other factors that may be just as important or even more important. Even when evaluating sound reduction, tone and pitch sometimes makes a bigger difference than just absolutely volume production. There are theoretical methods of shifting the sound to frequencies outside of the human ear range. Flash reduction is a major factor, especially in low light shooting.
Size and weight are critical factors to consider. Given that the weight is hanging off of the end of a barrel, which could be very long, the weight that you would feel handling a weapon with a suppressor can be very sensitive to weight. Also a longer suppressor would shift the center of gravity, even further out from the shooter, and also make the firearm more difficult to maneuver in close quarters or around barricades. For this reason, a lot of companies are moving towards squatter and thicker models. This works for long guns, but for pistols that require sights to clear the edge of the suppressor, it may not be an option.
Another factor is flow through versus baffled design. Baffle designs tend to be gassier, causing more forceful action of the bolt or slide due to back pressure. If you do not have an adjustable block or a charging handle designed to vent gas, you may want a flow through design. Lastly, I would say that IR and heat signature should be a factor. This was not previously a factor because all suppressors are made out of metal and they all heat up significantly during rapid fire. With polymer 3d printed suppressors, there’s a significant decrease in heat transferred to the outer wall of the suppressor. Given the increasing prevalence of night vision devices and thermal imaging devices, a metal suppressor is going to be easier to pick up. In addition, if you have ever burnt yourself on a metal suppressor, you’ll be surprised how cool a polymer suppressor stays.
Differences between traditional metal suppressors and printed polymer suppressors:
Obviously, there’s a huge difference between polymers (particularly commonly available FDM polymers) and the materials that are commonly used in metal suppressors (steel, aluminum, and titanium).
The first issue is pressure. A suppressor must be able to handle the expanding gas. This varies significantly based on caliber. 22lr has a very small amount of gas and the pressure is very easy to handle. 9 mm and other handgun calibers are obviously higher. Rifle cartridges are obviously even more challenging, particularly SBRs. Specifically 5.56 in a 10.5” or lower barrel is especially challenging because the bore on a baffle is quite a bit smaller than 30 cal. Another way to decrease the effects of pressure is to use a flow through design as opposed to baffled design.
There are two separate forces in the suppressor; the first is radial, or an outward expansion. The second is axial, pushing forward on the suppressor. The layer lines on a printed suppressor will always be the weakest point as the layer adhesion will never be as strong as a solid piece of filament. From a printing perspective, it is natural to attempt to print upright but from a material science perspective, it introduces problems.
The second problem is heat. PLA is especially sensitive to heat and is known to deform in a hot car. Printed suppressors are exposed to a massive amount of heat. However, unlike metal suppressors, polymers are more of an insulator. Because the impulse is very quick, and the conductivity is very low, actually a smaller amount of heat energy is absorbed and retained by a polymer suppressor compared to a metal suppressor. A single mag full auto through a firearm is enough to make a metal suppressor not safe to the touch, but a printed suppressor can still be held comfortably.
However, with prolonged fire, printed material, especially PLA will absolutely soften and start to deform. This causes traditional cone type baffles to permanently deform when softened and exposed to a forceful blast of gas. Cones in particular are susceptible to this because the apex of the cone is far from the wall and has no support. Using K baffles helps significantly with this issue because the apex has more material and more support, not less.
My latest baffle design also utilizes two rods that help support the cone like an internal skeletal structure. In my testing steel rods actually did worse than unreinforced baffles because steel tends to retain heat.
The next problem is threading. There is a significant amount of forward force on the suppressor due to the expanding gas pushing forward. The DMD9 was the first use of a thread adapter, which works well for handgun and rimfire calibers but starts to be a point of failure for centerfire rifles. Earlier models also used KAK and Breek forwarding cans encased in resin, and now we are using hardened steel rods. There is a need for a universal QD muzzle device mount in 3d2a to make it easy for developers and builders
My personal design philosophy:
I aim to use as little printed material as possible. Any weakness of PLA should not be addressed by just adding more PLA. I know there are people who value 100% printed suppressor that requires new post processing. My work is not that.
3D printing excels at creating geometry that is hard to replicate by conventional subtractive method of manufacturing. It does not use the strongest material.
Anywhere I can replace printed material with another material, I will. The weight/strength trade-off is always favorable.