Yes, it can be legal to make a silencer. For everything Form-1, from silencer designs that are easily made, to filing forms with the BATF, to 3D modeling. Remember, you must have an approved BATF Form-1 to make a silencer. All NFA laws apply.
I got the approval for a shot gun suppressor from my wife. All I need now is the ATF to agree. After stamp approval I plan on porting a barrel extension. (7-9" length) I will weld on a nut on the originsl barrel right in front of the gas block to make the full length of the original barrel the expansion chamber. The diameter is going to be 2.5-3 inches.
My first question is on tube material. I heard that some have used aluminum cans on pistols. As the gas pressure of a shot gun is a 4th of a pistols it seems like this would be a good choice of material to build the tube out of. Aluminum 6061 seems to be a good choice. Thickness? Would I be able to use .06" thickness on a 2.5" tube?
This will be an on going thread, so any formulas and resources you could offer would be appreciated.
I used 2" OD x 0.065" wall aluminum tubing on my shotgun suppressor. Everything was 6061 aluminum except for the 304SS mount. The low pressure and large more make it a challenge to get the gas to go where you want it. Mine is 12" long and works well. I ended up anodizing all the baffles.
Wow, that's a slick looking and sounding supressor. What else can you tell me about it? Do you know what kind of dB rating you are getting vs un suppressed? Have you had any baffle strikes? Is there a limit to the ammo you can use? Have you run it wet? Do you have any suggestions for my build?
If you use aluminum, I would recommend using 7075 (T3 or higher) for your material. It is much stronger that 6061. It's used in aircraft fittings that require the strength of steel, but low weight. In fact, it's strength is similar to that of 304 and 316 SS. It's an excellent material to work with and is structurally the strongest aluminum alloy that is readily available and relatively inexpensive. I don't know if you'll need the extra strength, but why take the chance and wonder? The only thing I would caution against is fatigue. Aluminum doesn't take high temperatures very well and fatigues quickly at higher temps. It may look fine one day, and fail the next. However, in a shotgun, with it's lower pressures, you may not see any issues. Particularly if you're not doing mag dumps. But for you average slow fire, hunting, etc., I would think it should work nicely. One piece of advise, if you use aluminum, be sure to use alodine (or some other acid etching) before painting. This creates a corrosion barrier and prevents it from corroding unseen beneath your paint. Alodine is available from any aircraft parts supplier.
Superq7 wrote:Wow, that's a slick looking and sounding supressor. What else can you tell me about it? Do you know what kind of dB rating you are getting vs un suppressed? Have you had any baffle strikes? Is there a limit to the ammo you can use? Have you run it wet? Do you have any suggestions for my build?
I have no clue on actual decibels since I have no way to accurately measure. I haven't shot it wet yet but it should be even quieter when I get a chance too.
My design uses tapered bores in the baffle to keep the wad shut so any traditional wadded shells works in it.
Superq7 wrote:Wow, that's a slick looking and sounding supressor. What else can you tell me about it? Do you know what kind of dB rating you are getting vs un suppressed? Have you had any baffle strikes? Is there a limit to the ammo you can use? Have you run it wet? Do you have any suggestions for my build?
I have no clue on actual decibels since I have no way to accurately measure. I haven't shot it wet yet but it should be even quieter when I get a chance too.
My design uses tapered bores in the baffle to keep the wad shut so any traditional wadded shells works in it.
Excellent thanks, I have a 410 that I have been experimenting with, I never thought of tapering the baffles to keep the wad closed.
When I get through my other cans I will get that out again
Cheers
D
Of all the things I've lost it's my mind I miss the most
All I need now is the ATF to agree. 
After stamp approval I plan on porting a barrel extension. (7-9" length) I will weld on a nut on the originsl barrel right in front of the gas block to make the full length of the original barrel the expansion chamber. The diameter is going to be 2.5-3 inches. 
