Best AR-15 Builds: Garrow Arms .17 HMR

Today, I want to show you something unique in the AR-15 world…

What makes this unique isn’t the weird lower or some fancy accessory, but the upper and caliber.

This is the Garrow Arms .17 HMR upper receiver. What makes it unique is the fact that this isn’t a typical blowback rimfire upper. 

Instead, it’s a direct impingement roller delayed blowback system. It utilizes a unique and custom upper receiver and a very cool bolt carrier group.

Direct Impingement, Roller Delayed Blowback?

You may ask why? Why use a fancy system over a cheap and reliable blowback design? 

Most .22 LR AR-15s use a blowback design.

This simple and reliable system works well with the low powered .22 LR. However, when faced with the amped-up .17 HMR it runs into some difficulties. 

Rimfire guns can be dirty and a lot of blowback powered guns are quite messy and leave a ton of residue. When people shoot a lot, or fail to clean their rimfires they may experience a failure to go into battery and they could fire out of battery. 

With a .22 LR, it’s not a good thing to fire out of battery, but it’s nowhere near as dangerous as a .17 HMR cartridge. The .17 HMR is a hot little cartridge.

With the Garrow Arms design, the firing pin cannot make contact with the cartridge until it is fully in battery. 

Additionally, the direct impingement delayed blowback system makes the system more reliable when dealing with rimfire rounds. On top of all of that, a blowback system usually has a heavy bolt to function correctly.

The delayed nature of this system means the bolt can be lighter in weight. 

This lighter weight bolt means ultimately you have a smoother recoil impulse. 

Besides the net benefits, there is the cool and unique factor behind a direct impingement delayed blowback system. It’s unique in an AR platform and provides a cool factor unto itself. 

Garrow Arms Upper 

I’ve described what the upper is in terms of how it works, but let’s expand on it a bit. The Garrow Arms Upper is a billeted upper receiver that is completely proprietary to function with the unique bolt.

It does use a standard charging handle and a standard barrel nut. It features an 18-inch stainless steel barrel that’s threaded. 

The upper comes with a standard Hogue style round aluminum handguard, but there are optional Keymod and M-Lok rail systems available.

The upper comes with two polymer 10 round magazines that are the same size as standard AR magazines so they function with a standard lower.

The Garrow Arms Upper also comes with a custom buffer spring and a plastic plug necessary for the buffer system. Speaking of, you’ll use a standard buffer, but in an odd configuration.

The buffer goes in backward and it goes in before the spring. 

The plastic plug then goes into the buffer tube and acts as the buffer. It’s simple, and the gun will not run reliably if you do not do this. 

As the instructions say I lightly oiled the bolt prior to shooting and the bolt itself is easily cleaned with a slick finish.

Be aware that when you remove the bolt two balls will fall out with it. These steel BBs are necessary for the gun to operate, so catch those as they fall out. 

The bolt is incredibly lightweight and an impressive piece of machining. The design itself is quite unique and impressive. 

The upper is a flat top and the .17 HMR demands an optic. Additionally, I have the standard aluminum tube handguard design.

It’s simple, lightweight, free-floating and textured. Together the entire set-up is quite lightweight and easy handling. 

Why .17 HMR? 

We did a whole article on why .17 HMR is an awesome cartridge. Check it out here. 

I’ll give you a few bullet points as to why before we move on into the rest of the build. 

The .17 HMR is unlike most other rimfire rounds, it’s: 

• Insanely Fast
• Flat shooting 
• Accurate
• Capable of taking small game out to 200 yards! 

It’s a fun little cartridge. To be perfectly honest I don’t have a need for it, but I wanted a delayed blowback AR-15 and bam now I have a .17 HMR model.

The Rest of the Gun 

Of course, the Upper isn’t everything. We have an entire rifle to talk about. Let’s finish out the upper though. 

The Charging Handle 

I really have taken a shine to latchless designs lately and the Strike Industries model is affordable and efficient.

The Strike Industries Latchless charging handle uses a hidden spring mechanism that keeps the charging handle in place. 

You don’t feel that spring or any resistance in general when you charge the weapon. The Strike Industries Latchless charging handle is ambidextrous, compact, features an anodized black finish.

It can also be extended with an easy add on an attachment if you so choose. 

The Muzzle Device 

This is a weird one, and unfortunately, it seems like the company is long out of business. I can find an unused Twitter and Youtube channel, but no other presence. My muzzle device is a Quick Change Muzzle Adapter setup by Apex Predator Arms. 

This system was originally designed so you could easily swap muzzle devices on an AR tool-free. I had it in the parts bin and tossed it on. This is specifically a flash suppressor muzzle device. 

It’s not really needed if I’m not shooting in low light, but on the occasion, I am it’s a nice add on. Plus it gives those threads something to do. 

If you want something that’s still in production, anything simple would fit the bill such as a normal A2 flash hider or a SureFire 3 Prong Flash Hider!

The Optic 

The Optic is the always affordable and always awesome ProStaff 5. The Nikon ProStaff 5 is a handy little optic that I use for a variety of purposes.

Oddly enough I tend to alternate it between my AR-10, and this weapon depending on what I’m planning to do. 

The ProStaff 5 is quick and easy to zero and remains mounted on a one-piece Warne MSR XSKEL1 Gen 2 mount between guns. Both guns are somewhat niche in terms of how I use them, so I haven’t purchased another optic and mount. 

The Nikon ProStaff 5 comes in a few different magnification levels including 2.5 to 10X which I used on these guns. It’s perfect for the ranges I shoot at and it keeps the optic nice and light. 

The ProStaff 5 is remarkably clear and consistently accurate when you factor in the optic’s price tag. It’s not cheap, but it’s not a NightForce either. For most shooters, and for anyone with a .17 HMR the ProStaff 5 is perfect. 

The Lower Receiver 

Omni Hybrid Lower 

The Omni Hybrid lower is a method to mix polymer and metal to create a lighter and cheaper lower receiver. I picked this receiver up years ago for 35 dollars.

It took this long to make a rifle out of it because… It’s not a good lower. 

This is the second ATI Omni receiver I’ve received since the first was terribly out of spec. Specifically, the rear takedown pin’s hole was too big and the pin and takedown pin would just fall out. This replacement sat in the parts bin forever because of that.

Finally, when I built this gun I found the exact same problem to a smaller degree. The rear takedown pin will come out, but I have to wiggle and pull. It works well enough to function and shoot, but is still disheartening. 

I would never use it on a gun for serious use, but for a recreational plinker I’m okay with it. Plus, I’m not sending another lower back and spending another 6 bucks for a background check on the replacement. At that point, I’ve paid for a metal receiver. 

ATI did promise to provide a check to pay for the background check fee, and transfer fee. However, that check never came. 

The Omni Lower is light and does have a flared magazine well, as well as a built-in, enlarged trigger guard. All of the other parts snapped into place with ease and after a few hundred rounds the gun still handles like a dream. The lower receiver does nothing to impede reliability. 

For a cheaper lower that won’t leave you disappointed, go for something like Palmetto State Armory or Anderson.

Stock 

B5 systems make some awesome stuff and this gun wears my favorite B5 SOPMOD stock. The B5 as it’s called is an enhanced SOPMOD that’s slimmer and lighter than the original. It lacks storage compartments but is quite comfortable. 

It’s also rock solid and doesn’t wiggle or move. It provides an excellent cheek rest and is beard friendly. The B5 Systems stock has been one of my favorites long enough that it’s found its way onto three rifles. 

Not only is it comfortable, but it also provides a QD sling point and two additional sling ports for running webbing through. The B5 requires a carbine tube and gives you your standard 6 positions.

You can get it in a variety of different colors, including all the typical tactical colors. 

Lower Parts Kit 

I went with a stock standard PSA Mil Spec lower parts kit. Nothing fancy, and the trigger is perfectly fine for 200-yard shots.

PSA includes the Magpul MIAD grip in their LPK and I love it. The little storage compartment is perfect for my Operator Survivor Tool. 

How It All Runs

This is one of my most accurate guns when used inside .17 HMR’s range.

It makes tiny little groups that look like clovers at 100 yards. This was an in the prone position with a stabilizing bag. That kind of accuracy is a must-have for this gun. 

When it comes to varmint hunting you are trying to hit a small target that can literally be squirrelly.

You have to demand top-notch accuracy from a rimfire hunting rifle designed for small animals and the Garrow Arms Upper delivers it. 

Reliability wise I’ve yet to run into any failures across a variety of ammunition related to the gun. You get the occasional failure to fire, which is more or less a symptom of rimfire designs.

Extraction, ejection, and magazine feeding have been perfect so far. 

I’m at two years of ownership and fired quite a bit through the gun.

I initially paired this upper with one of my standard AR-15 lowers and just swapped uppers and swapped buffers around. Earlier this year I decided to make a dedicated lower for the Garrow Arms upper. 

Since then I’ve gone through 250 rounds of .17 HMR without any issues beyond failure to ignite on occasion. The gun runs together in perfect harmony and puts lead where leads needs to be. 

What do you fine folks think? Garrow Arms also has plans for a roller delayed .22 WMR and potentially a 9mm upper in the future. Do those appeal more to you? Let us know why below. For more small-bore AR-15 action, take a look at the Best AR-15 in .22LR.