Garrow Firearms Development .17 HMR AR15

A roller-locked gas operated .17 HMR AR15 upper? You have my attention. Garrow Firearms Development is announcing the availability of a complete upper receiver group for the AR platform that allows for the use of all milspec triggers. At a reasonable $599 price point, semi auto .17 HMR is within reach.

I recently had the chance to experiment with suppressing the .17 HMR cartridge with the Bowers Group USS 22 from Silencer Shop. And I was pleasantly surprised – the hot little rimfire round obviously was supersonic, but the crack of the bullet was much farther forward of my shooting position in comparison to a supersonic .22LR. In my opinion, the Bowers USS is probably the quietest silencer for .17 HMR currently on the market.

Let’s take a look at the Garrow upper:

Garrow .17 HMR AR15 Upper Receiver Group – $599

The GFD AR 17 HMR fires from a gas operated locked bolt system eliminating the dangers of blowback actions. It is designed to prevent the firing pin from hitting the cartridge unless the bolt is locked in battery an important safety feature.

Why is it gas operated?

The 17 HMR cartridge is a popular rimfire round. It is made on high speed machinery producing millions of rounds each month. Vendors supply cartridge cases, bullets, powder, and priming compound to manufacturers which can have lot to lot variations. It is a small capacity cartridge so small variations in manufacturing can make a big difference. As an example a 1/10th grain difference of priming compound can vary pressure. The result can be that most of the cartridges fall under a bell curve within manufacturing tolerances and some pressures will be outside.

Blowback actions can be unreliable since the bolt needs to be light enough to operate at the lower extreme spread yet heavy enough to keep the case-head from separating with a hot round.

How does the GFD 17 HMR Upper Assembly address these blowback problems?

The GFD Uppers are designed too leave the bolt locked until the bullet passes the gas-port in the barrel releasing a small volume of gas to unlock the bolt when the pressure reaches a safe level.

GFD built in safety features:

• the firing pin can not reach the cartridge until the bolt is locked in place
• in the even of a case-head failure the gas is designed to escape down and out through the magazine well. Remember, safety eye wear and hearing protection are always recommended.

GFD AR-17 HMR benefit features:

• since the GFD Upper Assembly does not depend on inertia to operate a much lighter bolt is used allowing for a more forceful extraction cycle
• the GFD lighter bolt makes for a more stable firing cycle since there is less recoil impinging your sight picture than with a heavier bolt
• it has a patent pending gas operated design that is simple and reliable making it one of the most advanced rimfire on the market




LE – Science – OSINT.
On a mission to make all of my guns as quiet as possible.
Twitter: @gunboxready
Instagram: @tfb_pete


  • Giolli Joker

    Ball locking.

    • Brett baker

      Kind of what Savage did on the A17.

      • gunsandrockets

        Not really. A17 is a delayed blowback.

        • ostiariusalpha

          Interrupter lug delayed blowback. Hesitation locks actually halt the bolt’s rearward movement for a moment, whereas the interrupter lug merely slows the cycling as it is cammed into the bolt group.

  • marinepride

    Color me interested

  • Holdfast_II

    Interesting for CT where rimfires are allowed one more “evil feature” than center-fires – so if you weld a muzzle brake and have a non-adjustable stock, this could be legal.

  • Christian Hedegaard-Schou

    Good choice for CA where this would be legal without a magazine lock as rimfire rifles are exempt from the assault weapons legislation there.

    • Haulin’ Oats

      Alexander Arms has been offering a 17 HMR AR 15 for years now.

      • Christian Hedegaard-Schou

        However, they used to require it be sold with a bullet button, showing that they don’t actually understand the law.

        Not that you couldn’t remove it.

        And more importantly, why does that not make this a good choice? Isn’t more options always a good thing?

      • Ours is made to prevent firing out of battery, a significant safety feature. Also fires from a locked bolt, making it very reliable and accurate.

    • iksnilol

      Why doesn’t someone make a .223 rimfire?

      • Haulin’ Oats

        They do, it’s called 22LR.

      • Christian Hedegaard-Schou


        Case heads on rimfire rifles must be thick enough to contain the pressure of the cartridge (55kpsi for .223/5.56), but thin enough that the action of the firing pin can crush them in order to set off the priming compound.

        If you made a 55kpsi rimfire .223 clone, your first shot would lead to a ruptured case, putting all that power and explosion into your face instead of being used to push a bullet down the bore.

    • gunsandrockets

      My first thought.

  • Dan

    Do the balls engage in a steel trunion or insert inside the upper? Is the upper made of steel? I’d be interested to know what the rollers engage in. It can’t be in the aluminum of the upper, can it?

    • Dan

      Ahh, it looks like maybe there are steel inserts threaded into the upper?

    • You are right! 4140 tool steel inserts lock the rollers.

      • Dan

        You are a genius, sir! Beautiful design. Now you should make some of these in pistol calibers. Straight blowback in 9mm, 45, and 10 leads to heavy bolts and ejection port bark when running suppressed. But they don’t provide enough gas for reliable cycling. Maybe a 7.52×25 while I’m dreaming….

      • noob

        Ball bearings! that’s genius. Why are most German roller locking systems cylindrical shaped? Ball bearings seem to be an easily replaced commodity item while cylindrical or barrel shaped rollers are a part you need to spend time machining to shape.

      • Christian Hedegaard-Schou

        Please please please make a variant in 10mm….

        Blowback is just not good enough for the 10mm.

        • You’ll just have to see what’s in store for the future 😉
          Maybe an AR-15 that’ll fit in a purse (…or a “man bag”)? lol

    • Shankbone

      I don’t know what any of that means, but it sounds like the “dog knot” of robot reproduction.

      • Dan

        Basically that’s what it is haha.

      • Well… it runs better wet, it ends in a bang, but the… gas discharge is what keeps it going. Some robots just swing that way :x)

  • Cymond

    I really want to know more about that gas system. I’m only familiar with piston and standard AR-15 (not truly DI) gas systems.

    Does this mean it’s a truly Direct Impingement system?

    • Well, direct impingement means: a gas-operated firearm that directs gas from a fired cartridge directly into the bolt carrier or slide assembly to cycle the action. Or, at least that’s what my patent attorney tells me… and Wikipedia 😉

      • Haulin’ Oats

        What kind of buffer does this upper use? Will it work with my standard rifle length buffer or carbine h2?

        • It comes with a derrlyin buffer and spring made for the system. The short answer is: Yes. It works with any buffer system. In the manual is a set of instructions that will explain how to use your existing buffer as a spacer.

          • chase

            Any chance “any buffer system” includes the rat-tail of the Ares/Fightlite SCR?

          • Haha
            You got me there.
            That is not really mil-spec though….

          • chase

            I can dream. I’d love to see a non-blowback pistol caliber upper I could put on mine. This is still really cool though

  • Tinkerer

    By the gods! Something unusual and interesting in the AR world!

    • I’m glad you think so 😉
      It was actually the main reason I decided to invent something for the AR before other firearms; there was a clear niche and lack of innovation over decades.

  • Haulin’ Oats

    Why is your rifle then limited to only 10 round magazines? Where’s the 100 or 200 round “standard capacity” magazines?

    • Christian Hedegaard-Schou

      You do realize that for a state like CA, 100rd “standard capacity” magazines are still illegal, right?

      • Tassiebush

        Does that apply if it’s a rimfire?

        • Christian Hedegaard-Schou

          It doesn’t matter what kind of cartridge it holds. “Large capacity” magazines are illegal in CA. Period. Full stop. Rimfire, centerfire, rifle, pistol, doesn’t matter.

          “Large capacity” is defined as anything that holds more than 10 rounds.

  • Person

    I can’t wait for them to step up and do the .17 WSM, if only to give our CA and CT friends some more horsepower.

    • gunsandrockets

      Exploit the full potential of that locked rimfire action.

    • William M Durham

      They have more firepower, its called being a gang member , as they can carry ak-47’s around like old men carry walking sticks. The police in most city areas of California are scared of the gangs and their fire power which all comes across the [so well controlled border] where anything can be had for a price from ak’s to m-60’s, if the mexican army has it you can buy it, but only if your are a gang member . If the normal California white boy even tried to but an AK his ass would be under the jail. Just loved the National Geographic special on the gangs of California, the camera men were so afraid they would be shot they actually shook the new special cameras they had with the anti-vibration feature. And they did actually film California cops, in the Oakland area looking at the several gang members standing on the corner as they were driving by until the gang members flashed their { 3 } AKs at them then the [police car grew wings and flew out of sight. That’s what I call a police farce. Gun laws so harsh that a normal citizens can only see an AR/AK on TV unless they see the gang members guns which are always shown and flaunted and the cops run and hide. Really sad, but all the politicians live in gated communities and have armed security paid for by the poor over taxed people. Sorry for going off but just couldn’t help myself as California is a funny word to Americans.

  • civilianaf

    Oh Hell yes! So much want!

  • ozzallos .

    What’s the application for this? No, seriously, I’m curious and don’t have a clue.

    • 22winmag

      Tree rats at 140 yards.

      • Shankbone

        Sage rats at one-fiddy.

        • Sixshot6

          Not tree rats at tree-fiddy?

    • Mainly, it’s a varmint cartridge. You can use it at pistol ranges since it’s rimfire, and it’s great for target practice because you’ll save quite a bit on ammo and wear & tear that you’d be spending on your expensive uppers. People are using it in 3-gun competitions because of the minimal recoil (and winning them too ;).

  • Choogisaurus Rex

    Imagine this on a FA lower

  • gunsandrockets

    Remember the old TRW Low Maintenance Rifle? It used a gas operated roller locked bolt too, though I imagine very different in detail from this new AR upper. Since the LMR for one thing was open-bolt full-auto only.

  • Sixshot6

    Are you going to do a 22wmr version? In the uk it’s the most powerful semi we can have.

  • uzimandias

    Now if they’d only build it in .17 WSM, and if Winchester would only top that cartridge with a 30-gr bullet, then we’d have something really useful.

    • Tassiebush

      I’m pretty sure that the 20grain 17wsm loads have more energy than the 25grain ones so 30grain probably isn’t as good an idea as it initially seems. Sorry to kill a dream 🙁
      On the other hand I guess at least there is the benefit of lighter ammo! (please note I could be remembering wrong)