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How I Built a 300 AAC Blackout Suppressor

(and a .22 suppressor too)

By Major Rob Robinette


Warning: You must have a BATFE Form 1 with tax stamp before you start to legally build a suppressor. National Firearms Act (NFA) rules apply and you can do hard prison time for violating the law.
The first step in manufacturing a suppressor is getting permission from the Bureau of Alcohol Tobacco Firearms and Explosives (BATFE) by filling out a Form 1 and sending in $200 for a tax stamp. It will take about 5 months to get the tax stamp so send it in early.
Since I had a combo lathe/mill at home that I used for making car parts I already had everything I needed to make a suppressor. I decided to go with an all aluminum "monolithic baffle" design for this 300 Blackout suppressor. The 300 Blackout uses standard .308 size bullets and has fast spin rifling to stabilize heavy subsonic bullets. It's very good at sending heavy 220 or 240 grain bullets at subsonic speeds downrange accurately. The 300 Blackout can also be loaded for supersonic and makes an excellent home defense and deer rifle.
If I were building a suppressor for .308 supersonic loads I would use at the very minimum steel for the blast baffle (first baffle the bullet encounters). An all aluminum suppressor should only be used with subsonic 300 Blackout or .308. Supersonic rounds will wear away the aluminum baffles.
I have used this suppressor on several .308 rifles using subsonic 175 grain Sierra MatchKing bullets and Trail Boss powder. Subsonic .308 loads are very mild and a thick aluminum blast baffle is fully adequate. I used 175 grain bullets because standard .308 barrels do not have the fast rifling needed to stabilize heavier bullets.
I used 1.5 inch outside diameter round aluminum bar for the baffle and 1.5 inch inside diameter aluminum tube for the baffle cover. I used 6061 T6 aluminum bar and tube from www.metalsdepot.com The 1 foot long bar used here cost only $12. The suppressor is 8 inches long.
To manufacture a monolithic baffle suppressor the basic steps are:
    Start with a solid round metal bar to make the baffle

    Cut the bar to length

    Face both ends of the baffle on the lathe
    You may need to remove some material from the outside of the baffle so that it will fit inside your aluminum tube, but don't take too much because you want a nice tight fit.
    Drill the bullet path through the baffle
    Drill and tap one end of the baffle where the baffle will screw onto the threaded barrel
    Drill/mill out the gas chambers in the baffle
    Face the ends of the seal tube
    To finish the seal tube you can remove a small amount of material on the lathe or simply polish it up with some steel wool
    Insert the completed baffle into the metal tube and seal. The seal can be a press fit, welded, epoxied or even duct tape!
Don't forget to inscribe or engrave the suppressor with:
        Serial #
        Model #
        Manufacturer (your name or trust name)

        Manufacturer's city & state

Building the Suppressors

Using the Grizzly lathe to drill the baffle's center hole.

 

To prepare for tapping I drilled the thread end of the baffle.

 

Drilling the bullet path the full length of the suppressor. For a .308 bullet I used an 11/32" (.344") long bit from Home Depot. For a .223/5.56 use a 1/4" (.250") bit.

 

Boring the thread end to the pre-tap size. This is not necessary if you have a 9/16 inch drill bit for 5/8x24 thread (standard for 300BLK and .308 rifles) or 7/16 inch drill bit for 1/2x28 thread (standard for .22 and .223/5.56 rifles).

 

Tapping the baffle--Do not try to use the lathe's power to do this. I used the tailstock to simply hold the tap for perfect alignment with the bullet path. I pushed inward on the tailstock and turned the lathe chuck by hand to start the tap. I did the last half of the tap using a standard tap hand wrench so I could feel when the tap bottomed out. I used a 5/8" x 24 threads per inch (tpi) tap to match the thread on my 300 Blackout barrel. For a normal .22 or .223/5.56 rifle use 1/2" x 28 tpi.

 

Drilling and milling the baffle chambers. Note the marked baffles to be milled out. I started with a drill bit then finished up with an end mill to finalize the baffle chamber shapes.

 

Cleaning up the bullet path after milling.

 

The finished baffle. I had to turn the baffle in the lathe to remove about 15 thousandths from its diameter to make it fit easily into the tube. I intentionally left the baffle chambers odd shapes to disrupt the gas's path through the baffle. I now recommend heart shaped baffle chambers like in the .22 suppressor shown below because of how well that shape worked in controlling the gas.

 

I slid the completed baffle into the aluminum tube and welded both ends to seal the suppressor. It's now ready to be screwed onto a rifle, inspected for barrel alignment and test fired. Please forgive the crude welding, I'm an amateur aluminum welder. You'll need an AC TIG welder to do this kind of work. If I need to open the suppressor I can use the lathe to cut the welds to remove the tube cover. If I were to do another 300BLK suppressor I would go with a press fit like the .22 suppressor I shown in the next section.

 

The suppressor wrapped and installed on the 300 Blackout upper. The wrap helps reduce noise too.

 

A .22 baffle made of 1 inch solid round aluminum bar. Note the large square blast baffle at the bottom and the heart shaped gas chambers. This suppressor worked out very well and is quieter than a commercial .22 suppressor I purchased later. The baffle is 6 inches long.

 

The .22 baffle next to it's outer seal made from aluminum tube with a 1 inch inside diameter

 

The .22 baffle inserted into the tube seal with a nice tight press fit.

 

The .22 suppressor installed on my Ruger 10/22

Warning: You must have a BATFE Form 1 with tax stamp before you start to legally build a suppressor. National Firearms Act (NFA) rules apply and you can do hard prison time for violating the law.

By Major Rob Robinette

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