Anyone build a suppressor on a Form 1?

**Fudmottin** · January 28th, 2009, 05:33 PM

I was going to ask here:

http://www.quarterbore.net/forums/forumdisplay.php?f=40

But the activity there is rather low compared to here.

I'm curious as to whether anyone has built a suppressor on a Form 1 and how they came about the design you used. I know the basic principles are simple enough. The technical details are another matter. For example, how large do you need to make the aperture so that you won't get baffle strikes from the slug wobbling a bit?

The bottom line is that it seems like buying on a Form 4 is going to be cheaper in the long run (unless the value of your time is zero). So you either build because you think you have a better design or some other reason. I would like to know that too, if you care to share.

The NFA makes experimenting with ideas really expensive. Making a single baffle seems to be all you need to do to be in violation if you haven't received your approved Form 1 with stamp yet.

**evilfij** · January 28th, 2009, 05:36 PM

I saw plans and am considering it, but I have not looked into it beyond that.

**Fudmottin** · January 29th, 2009, 05:21 PM

Where did you see the plans? Is there a URL?

I'm also in the "considering it" stage. I've got a number of prerequisites to fulfill in order to actually seriously decide if I'm going to file a Form 1 or not. Among these are acquiring and learning to use the machine tools required for the job such as lathe, mill, and mig/tig/etc welding equipment.

Learning to use these tools has been something I've desired for some time now and I will be looking for schools in my area that teach this stuff.

**Mtdew** · January 29th, 2009, 07:19 PM

Unless you allready have a lathe, or complete unrestricted access to a lathe it's easier and cheaper to buy one.

Also you need a very good understanding of how they work before you can build one.

Your best resource will be: www.silencertalk.com silencersmithing section.

any "plans" you see on the net will be IMHO garbage

**Fudmottin** · January 31st, 2009, 08:15 PM

Originally Posted by Mtdew

Unless you allready have a lathe, or complete unrestricted access to a lathe it's easier and cheaper to buy one.

Also you need a very good understanding of how they work before you can build one.

Your best resource will be: www.silencertalk.com silencersmithing section.

any "plans" you see on the net will be IMHO garbage

I know it's easier to just buy one. I signed up for Silencer Talk.

Let me tell you my understanding of how a silencer works. Then you can tell me if you believe I have some sort of understanding on how they work. My description will not include anything to do with fabrication as there are things I need to learn and can learn about working with metal and using the appropriate tools (yes, all this would be work that would probably take as long as getting a Form-4 approved).

A silencer attempts to convert the hot, supersonic flow of muzzle gas into a cooler, subsonic flow. This results in noise reduction.

The simplest possible silencer would be a simple tube with two end caps. One screws onto the muzzle, the other lets the bullet through and the gas out. When the bullet clears the muzzle, the gas fills the chamber. This results in adiabatic cooling of the gas. The gas slows down a bit and is allowed to exit the front end cap through the aperture for the bullet. The only heat lost in this process is to the tube, end caps, and atmospheric gas in the tube. So the gas has about the same energy even though it is running cooler and at a lower pressure.

A single baffle can be added to this system. The baffle could be a simple disk with aperture for the bullet. Now you have two expansion chambers. You also have turbulence generated by the baffle as gasses pass through the aperture. Creating turbulence requires energy which comes from the heat in the gas. The baffle also acts as another surface to absorb some heat energy.

Multiple baffles would increase the amount of turbulence and heat loss from the muzzle gas. They would add additional surface area to absorb heat.

So a relatively crude but reasonably effective silencer would contain an initial expansion chamber to reduce the temperature and pressure of the muzzle gas, followed by a series of baffles with a single aperture to let the bullet pass through. Each aperture would create turbulence in the flow of the gasses and removal of heat from the gasses.

Improving on this design would involve finding ways to increase the turbulence in the gas so as to effect as much energy/heat loss as possible before the gas exits the front end cap. The cooler and slower the gas is at exit, the quieter the report.

If you know the length and diameter of the barrel's bore, you can effect further noise reduction by harmonically tuning the silencer to create sound wave cancelation. This bit is tricky.

This is my somewhat simplified understanding of how a silencer works. How close am I?

**Mtdew** · February 2nd, 2009, 09:56 AM

Closer than about 99% of people that post "Hey I want to build a silencer"

**Fudmottin** · February 2nd, 2009, 11:53 PM

I have a reasonable understanding of the gas laws and thermodynamics. Equally important things like fluid dynamics and acoustics are another matter. The primary reason I would want to build a silencer is for experimental / research / learning purposes. I fully plan to purchase another silencer on a Form 4.

It really sucks the way the rules are setup for making a silencer legally. There must be many ways to design baffles and the inner surface of the main tube. eg, does creating a few large vortexes with laminar flow work better than creating many smaller vortexes with non laminar flow work better?

You already pointed out the lack of reliability of any plans that may exist on the Internet. I certainly agree with you on that point. I would want to test a number of different approaches. Legally I can't do that without lots of Form 1s or a Class 2 license.

Not a very conducive environment for individual development, is it?