Good afternoon friends and welcome back to another edition of TFB’s Silencer Saturday brought to you by Yankee Hill Machine, manufacturers of the YHM R9 suppressor. Last week got to spend some time with the impressive CGS Hydra rimfire suppressors. This week we get our hands dirty with the manufacturing of a legal oil filter suppressor. Is it worth the NFA Form 1 application time and $200 to make one for yourself? Let’s take a look.

I picked up the new S&W M&P 15-22 retail from GrabAGun.com.

The new Gemtech Integra 15-22 integrally suppressed rimfire upper is just in for review from Smith & Wesson.

Form 1, EForms and more @ TFB:

• SILENCER SATURDAY #121: Build Your Own Form 1 Suppressor – Part 1
• My First ATF EForm 1: Easier And Faster Than I Expected
• TFB TUTORIAL: Using The ATF Eforms NFA Application System
• SILENCER SATURDAY #165: The NFA Registry – 2021
• ATF NFA Marking Requirements: Get. It. Right.

Making The Oil Filter Suppressor – The Fine Print

Listen, I wish we were all legally able to build silencers, short barrel riffles and machine guns without lengthy registration forms, $200 taxes and the threat of criminal prosecution. The unfortunate reality is that, unless we are thrown into a Mad Max or The Road type post-apocalyptic situation, violating the laws and regulations of the National Firearms Act can land you in serious trouble. Before you take steps to make any NFA item, do your research.

As a reminder, there is a difference between a licensed manufacturer and a Form 1 maker of NFA items. Manufacturers can make repairs and replace parts without the potential for creating a taxable event. Form 1 makers on the other hand, can be required to submit another application and pay another tax for the ability to replace a part on an already registered silencer.

Most importantly, safety is always the primary concern. Using equipment outside of its intended purposes can result in injury or death. An oil filter on a rimfire rifle might be ok, but on the end of your .45-70 Henry it can quickly turn into flying pieces of sharp metal.

I urge all of you to know and understand the laws and hazards before you decide to make a regulated item like a suppressor.

SILENCER SATURDAY #173: The LEGAL Oil Filter Suppressor

Highlighted in movies and video games, the oil filter suppressor has the mystique of covert ops or improvised weapons warfare. My main questions have always been:

• How do oil filter suppressors sound?
• How long do they last?
• Are oil filter suppressors worth the steps required for an NFA Form 1 approval?
• If you are in a legitimate, improvised weapons situation, is an oil filter suppressor a viable option?

In an effort to avoid additional legal concerns, I am not going to point you towards places that sell parts that could be used to make an oil filter suppressor. In the days of e-commerce, everything is just a few clicks away. I decided to use a direct thread style mount and a longer, heavy duty oil filter for the tube and baffle section. Obviously, the options are endless.

Whether you are a manufacturer or a Form 1 maker, proper NFA engraving is required.

• LASER TAGGING: Firearm Laser Engraving And Marking – An Introduction 
• Triumph 30W Fiber Laser

In automotive or machinery applications, oil filters are subjected to constant mid/high pressure as oil circulates through paper or other media to remove debris and impurities. Typically, oil is forced into one chamber of the filter, passing through the media and exiting back into the system through another chamber.

The system is a bit different from the baffles inside a suppressor. Using this type of filter as a silencer, the large internal volume is the driving force behind the noise reduction. Which means that to be effective, oil filter suppressors will usually need to be large and long. That’s what she said.

If you’ve ever changed your own oil, you’ll notice that the bottom of the filter has one large threaded hole surrounded by a series of smaller holes. Without closing off those smaller holes, trapped gas can end up blowing back towards the shooter. My mount/adapter squeezes up against the rubber gasket, sealing everything up.

Drilling a muzzle end isn’t a necessity – using a subsonic rimfire round I punched a hole in the end of the filter. Caution, using a larger caliber or high velocity round to make the initial bore exit hole may cause an over pressure event, causing a rupture or explosion.

After the .22 caliber hole, I opened it up further using a single 9mm round.

Eventually, the oil filter is going to wear out. As a Form 1 maker, you are not legally allowed to replace the filter on your own. This needs to be completed by a licensed manufacturer. Stupid, I know, but that’s the law.

Sound Performance:

I have to say, the CCI QUIET Semiauto .22LR sounded fantastic in the S&W M&P 15-22 pistol. Action and bullet impact noises were all that I heard. Of course, it was a monster on the end of the tiny .22 AR-15 pistol.

Performance dropped off on the H&K MP5K-PDW, but it was what I would call “hearing safe” for short periods of time (a non-scientific opinion). Even when switched to fully automatic fire, the 9mm subgun sounded pretty good – like a large flag flapping in a heavy wind.

As for how long they last, after a few hundred rounds I’ll be cutting this one open so we can all have a look.

Bottom line, in a post-apocalyptic world where laws are non-existent and stealth could mean the difference between life or death, an oil filter suppressor is a more than suitable option for an improvised weapon. In a modern society bogged down by rules, regulations and taxes, my suggestion is to save your money and buy a commercial suppressor.

Have a great week, be safe and we’ll see you back here next weekend for another Silencer Saturday.

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Silencer Saturday is Sponsored by Yankee Hill Machine

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DEALERS: If you want your link to buy YHM suppressors included in future Silencer Saturday posts, email: silencers@thefirearmblog.com