July 30, 2013
By Patrick Sweeney
OK, we've had a bit of background, and we've worked with a few cans, it is time to open them up (figuratively and literally) and see what they are made of.
The basic suppressor is a tubular shell (although you can make it any shape you want, which some manufacturers do) with a clearance tunnel through, and some means to attach it to your firearm. You could make one simply as a hollow shell, but it wouldn't be very efficient.
The tube can be almost anything, with some caveats. Making one out of cardboard would be a real short-term proposition. Plus, marking it with a serial number would be problematic.
The tube is usually aluminum, steel, or titanium. The mounts are usually stainless steel, simply to avoid galling and corrosion with the threads of the barrel or mount.
The baffles are a particular problem, given their harsh environment. The blast of heat and particulates, and the heat-cool cycle puts a lot of expansion-contraction stress on the baffles and assembly. Also, the heating-cooling aggravates corrosion and/or oxidation.
We also have a small problem of using dissimilar metals in constructing a suppressor, in the form of galvanic reaction. Attaching metals with large galvanic differentials (known as the Anodic Index) can lead to accelerated corrosion. So, designers have to keep in mind that their "perfect"construction could be compromised by something so simple as water. Sweat and sea water are even worse here.
There is also the problem of expense. Making suppressors out of unobtainum might increase service life, but if the materials cost makes the end product cost 10 times as much, who would buy it? Beside DoD, of course.
The galvanic reaction is just part of materials. You have to assemble the various parts. You can't weld dissimilar metals. Sure, you can find ways to weld stainless to carbon steel (ugly, and watch out for expansion differentials) but steel and aluminum? Steel and titanium?
You have to thread dissimilar metals, and that raises other potential headaches. Galling of threads, expansion differentials, and differing reactions to solvents or cleaning agents can all be a problem.
Light, inexpensive, easy to work. You'll see Al listed in suppressors that aren't going to see severe work, such as in a .22 Long Rifle. Alas, aluminum lacks a lot of other attributes needed for suppressors. It has little abrasion resistance, it suffers heinously in the heat of a suppressor, and bends too easily. That last makes it unsuited as a material for structural strength in a "can"that might see heavy use.
It also must be matched to a mount system using steel, or stainless steel. Aluminum threads would wear too quickly, screwed onto a steel barrel, and buyers would complain. So, makers have to attach the aluminum more or less permanently to the steel mountings.
In the most modern applications, stainless will also be treated by the Melonite process, a nitriding process that makes the surface file-hard and highly corrosion resistant. With the proper alloying, it can be easy to machine, it is stable in medium temps, but suffers at extreme temperatures. One good thing; in the alloys used, and compared to the real high-tech metals, it is relatively inexpensive.
But when you get a suppressor up to heat-visible temps, it gets soft. As for durability otherwise, and corrosion resistance, it is great — just a bit heavy.
Forming it is pretty simple, as any machinist who has his union card will be quite familiar with it. It can be machined, welded, annealed and re-hardened in multiple steps without problems.
Light, corrosion-resistant, with moderate fatigue resistance and good crack resistance, the big problems with titanium are cost and machining. Anything that will stand up to aerospace use, in engines and airframes, and can be counted on in marine, petrochemical refineries and oil drilling, is going to be tough to shape. And since it is so useful in those applications, it will be pricey. Think about it; the titanium your suppressor maker used, had to be bought out from under the noses of Boeing, Airbus, General Dynamics and petrochemical companies by the phalanx.
This is the name you will read, again and again, when it comes to baffle construction. Inconel is a trademark of the Special Metals Corporation, but it risks in the firearms community of slipping into being a generic name. There is iron in it, but it has so much nickel, chromium and molybdenum in it, that it would be correct to say it is an iron-bearing nickel alloy.
The alloy commonly in use, Inconel 625, has 58% nickel, 20+% chromium, 5% iron and 8% molybdenum. There are traces, less than a percent each, of all the other usual suspects in ferrous alloys.
Why Inconel? Simple, it has high strength and toughness even at high temps (all the way to 1800° F) and rates high on corrosion, oxidation and fatigue strength. It was developed for turbine blades; jet engine and steam-driven high-pressure pumps.
The drawbacks are few, but severe. Inconel work-hardens at an impressive rate, so machining baffles is an interesting proposition. If you don't plan your cutting passes properly, you'll find the baffles-to-be have work-hardened so much the tool simply slides over the surface, dulled and unable to make the last cut. It also is a royal pain in the butt to weld, and has driven suppressor makers to develop/request new alloys of Inconel, and search for effective welding methods.
Making baffles out of Inconel is not for the machinist who makes your cool, billet-cut aluminum engine covers, and is not to be welded by the guy who attached your last trailer hitch.
All these materials can be, and are, improved with various heat-treatments, coatings, chemical baths during manufacture, and construction. There is no such thing as "plain old [fill in the blank]"used in any suppressor you can buy.
And before you start grumping about your favorite super-metal, and the fact that no suppressor maker makes their products out of your favorite, consider this; they really, really want to sell you a suppressor. If they thought your candidate would hold up, could be fabricated, and sold at a profit, they'd be making it. A lot of these guys are not just some garage mechanics: they have degrees in metallurgy, engineering, and they know their subject. Give them a break.
A threaded steel barrel, with a threaded aluminum end cap, on an aluminum tube. This will not last long, but durability might have been irrelevant to the original designer.
Wipes? Rubber wipes, for God's sake: what were the commies thinking?
This kind of plastic "baffle" stack makes the wipes look like NASA-level engineering.
But that doesn't stop some people from trying, shall we say, alternative materials. I recently visited a major European military museum, and spent some time down in the vaults. Kid in a candy store? Me? You think? Among the very interesting things I got to lay hands on, were a pair of fascinating Makarovs. One was completely "sterile." That is, not a mark to be seen, except for toolmarks. But, it was fitted with an extended, threaded barrel. Oh, we know what that was for, don't we?
The other was marked, and came with a suppressor attached. To call it old-tech would have been kind. The tube was a simple aluminum shell. It had aluminum end caps, the rear threaded for the barrel, the front threaded to the tube, and that held a muzzle wipe in place. The whole thing had a flat black paint job, about on par with what you could do in the backyard with an aerosol can.
Wipes are something you will not see in today's suppressors. Basically, it is a rubber end cap, one that the bullet squirms out through. The first shot makes the hole, the rest follow, and it keeps the suppressor "quiet." Not as quiet as a modern can, and at the cost of accuracy. But back when Nixon was President, it was high-tech.
Inside, this suppressor had a length of plastic rod, drilled down the middle, with vent holes drilled on the sides. It appeared to have been cut to length with a hacksaw, by hand. The guys in the museum had not yet had time to test it, and had not yet divined its history. I can't imagine for a moment it represented the height of technology even for the primitive Warsaw Pact ordnance departments, but then againâ€¦
They have promised to report back on how efficient it is, but we all just smiled and shook our heads at the thought of that. Best to still be wearing hearing protection, even for the mild 9x18 Mak.
You can have a lightweight suppressor, but you'll pay for it. It will cost you in some manner; lessened durability, caliber restriction, higher cost, reduced decibel reduction from a heavier one, or a bigger chunk taken out of your wallet. The good news? You get to pick which cost you bear.