SILENCER SATURDAY #196: Coffin Mags and Ported Barrels – The B&T KH9SD

    KH9SD Ready to ventilate melons with the Suomi magazines

    KH9SD Ready to ventilate melons with the Suomi magazines

    Good morning ladies and gentlemen and welcome back to another edition of TFB’s Silencer Saturday brought to you by our friends at Yankee Hill Machine, manufacturers of the new YHM Phantom 22. Last week we dug into the Dead Air Primal on the Henry Model X in .45-70. This week, we head to Rusty’s neck of the woods to take a look at the B&T KH9SD equipped with their new RBS-9 Reduced Backpressure Silencer. Let’s dive deeper into B&T’s silent update to their awesome KH9 SMG.

    B&T @ TFB

    Editor’s Note: Thanks for piloting this week’s edition, Rusty! I’ll be back next week with a new release from a major manufacturer. Don’t forget to check out TFB’s Behind The Gun Podcast brought to you by Silencer Shop and Armscor.

    Silencer Saturday #196: Coffin Mags and Ported Barrels- the B&T KH9SD with B&T’s New RBS-9

    Ever since I saw the SITES Spectre in the hands of very serious gentlemen in Italy and Switzerland as a kid, I was a fan of the platform.  The look was very unique, and as I got to know more about submachine handguns in general, it always occupied a place on my “someday” list.  I was aware of the KH9’s Spectre lineage, yet sadly missed out on the first run of KH9’s to come stateside.  Every so often, I was checking on availability/possibility of another production run, when I saw a result pop up on Tar Heel State Firearm’s site with a new, very quiet variety of KH9.  The KH9SD was soon to be available.  I did not miss out on this run, and ordered one complete with the collapsible stock kit.

    B&T @ TFB:

    Out of the Box:

    The B&T KH9SD comes with B&T’s large hardcase for their pistols/smgs.  Inside the case was their nice cleaning kit, an adjustable single point sling with hook attachment, one 30-round APC9/TP9 B&T polymer magazine, and the KH9 itself.  Depending on how you order these, they come either with an endcap, a brace, or if you want to make the KH9SD into a two-stamp gun, a stock kit.  I filed a form 1 to make mine an SBR for use of the stock.

    KH9SD before stamps...

    KH9SD before stamps…

    and after!

    and after!

    First Shots:

    While I was waiting for paperwork to clear and for the Suomi coffin magazine adapter and suppressor to ship to my FFL, I initially tested it out with the polymer magazine magwell.  Though the 4″ barrel is ported, B&T thoughtfully included a barrel nut to block the ports that threads on the rearward portion of the barrel where the suppressor attaches.  Just don’t run your hand all the way forward on the handguard in this configuration, as it runs out further than the muzzle when there’s no can on the gun.

    B&T KH9SD Ventilated 4" barrel

    B&T KH9SD Ventilated 4″ barrel

    I had a great first range trip with the KH9SD.  Even without a stock and suppressor, I had good accuracy and the controls were intuitive.  The KH9 has no safety, but can be decocked via a lever on the side of the receiver.  Once decocked, the initial double action trigger pull is very heavy, and will prevent most accidental discharges.  Subsequent trigger polls are quite light, and provide for precise shooting.

    The KH9SD has a 2-stage, 2lb 11oz trigger when cocked.  There is 11oz of takeup in the first stage, and the second stage takes the additional 2lbs to break.  While reset is long, the trigger is smooth where it needs to be and crisp where it needs to be.  It won’t post the fastest split times, but is an excellent SMG trigger.

    Going Quiet:

    When the fortuitous day came and I could both throw on the stock and the suppressor came, I was pleasantly surprised to discover that the KH9SD would be equipped with the new 9mm version of B&T’s RBS reduced backpressure suppressor, previously only available for .223 caliber firearms.  For a blowback firearm, reduced backpressure would be a boon indeed.

    B&T KH9SD vent cooking nut and RBS9 suppressor

    Of course, the first ammunition I tried out with the suppressed KH9SD was Federal 150grn Syntech, a subsonic 9mm load.  I was not disappointed at all.  I don’t have metering equipment access like Pete or Austin, but not only would I describe the KH9SD with RBS-9 as “hearing safe”, I would go further and call it “hollywood quiet”, or “nailgun quiet”.  It sounds like a pneumatic nail gun to my ear.  With other 9mm loads, the KH9SD was pretty quiet but I would recommend earpro for more than several shots.

    note vent holes on the B&T RBS-9

    note vent holes on the B&T RBS-9

    B&T RBS-9 Reduced Backpressure Suppressor, it looks a bit like a potato masher grenade!

    B&T RBS-9 Reduced Backpressure Suppressor, it looks a bit like a potato masher grenade!

    Despite the 4″ vented barrel, muzzle velocities were as follows with the following loads:

    • Federal Syntech 150grn: 846fps
    • Black Hills FMJ 115grn: 1078fps
    • Israeli SMG +P+ 115grn: 1085fps
    • Speer +P+ 124grn: 1114fps

    The reduced backpressure from the RBS-9 made for very little gas coming out of the ejection port compared to other suppressed SMGs I have fired.  It was very pleasant, and not once did I feel like I was in a cloud of gas or having gas blow back into my eyes.  My only gripe is that the KH9SD will not fit into the factory case while suppressed.  I’ll just have to get a cool low profile nylon bag/case for this neat little SMG.

    It won't fit with the can attached!

    It won’t fit with the can attached!


    I found the KH9 to be capable of 1.5-2.5″ accuracy with most loads at 50 yards with the provided polymer flip sights.  Its favorite load accuracy wise was Federal HST +P 124grn.  The accuracy was good enough to consistently hit plates out at 200 yards, though I’m sure subsonic 9mm has questionable efficacy at that distance!

    B&T KH9SD VS APC45

    B&T KH9SD VS APC45


    In the course of 500 rounds fired so far, I have only had three failures to fire, possibly due to bad primers, being that I was using a huge variety of 9mm ammunition.  The KH9 likes all the 9mm ammo that you can feed it, including old steel case Brown Bear and 1970’s vintage Israeli SMG ammo I had lying around.  I fed over 15 different loads through the KH9SD, and it did not have significant issues with any of them.

    overbarrel end of the suppressor

    overbarrel end of the suppressor

    Cleaning and Disassembly:

    Cleaning the KH9SD was pretty easy.  One makes sure the firearm is unloaded, and then removes the trigger group via two pins.  Once this is done, one can click the endplate down and slide it out with the stock assembly attached.  The rest of the guts come out with removal of the cocking knob, including the bolt, striking mass, buffer, springs and endcap.  Thanks again to the RBS suppressor, cleanup was a breeze even after 500 rounds.

    B&T KH9SD disassembled for cleaning

    B&T KH9SD disassembled for cleaning

    Finnish Line:

    One of the coolest aspects of the KH9 platform is that you can easily modify the magwell to accept Suomi magazines.  I ordered up some 50-round coffin magazines, and installed the magwell adapter.  The adapter itself took 5 minutes to install.  Simply drive out the retaining pin of the B&T Maxwell, slide it off, and then torque and pin on the Suomi front and rear magazine adapter and magazine release, a process made all the easier due to an excellent receiver block that comes with the adapter.

    B&T KH9SD with Suomi magazine

    B&T KH9SD with Suomi magazine

    Out of 4 old Soumi magazines that I found in very good condition, I have one that is 100% reliable and the other three are getting there and should be 100% with a tad more cleaning and oiling.   The Suomi magazines worked well enough for me to run 200 rounds straight through the KH9SD, obliterating some watermelons that didn’t quite make it to ripeness.

    Overall Impressions:

    B&T’s KH9SD is an extremely well built, reliable, reasonably accurate and most importantly quiet re-imagining of the SITES Spectre.  I am very happy with my purchase, and look forward to using it in a PCC competition.  It’s also a great, very quiet platform to introduce new shooters to the 9mm cartridge.  Like most B&T products, it is expensive, but you do receive quality for the money.

    Objectively, it is well built, has decent accuracy, a light trigger, is compatible with two kinds of magazines,  has some of the least gas blowback due to the RBS suppressor, and is MP5SD-level quiet.  Subjectively, I find it to be one of my favorite new firearms, and the quietest 9mm host/suppressor combination that I have.  I have zero regrets with my purchase!

    Thanks to Tar Heel State Firearms for their excellent customer service and communication!

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    Rusty S.

    Having always had a passion for firearms, Rusty S. has had experience in gunsmithing, firearms retail, hunting, competitive shooting, range construction, as an IDPA certified range safety officer and a certified instructor. He has received military, law enforcement, and private training in the use of firearms. Editor at