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"AR-22" LTR build

Started by Newsletter, October 30, 2023, 06:35:26 PM

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"AR-22" LTR build
By: Willociraptor

Part 1/5 : Conceptualizing the Build
On the basis that I want a new rifle, a few foundational questions must be asked and answered.

Q) What do I want to do with this rifle?
A) I want to get more trigger time on AR-style rifles for less financial investment, doing things like Appleseed, Rimfire Challenge, and general-purpose plinking.

Q) Wider selection (platforms with pistol grips), or narrower selection (strictly AR variants)?
A) AR variants.

Q) What cartridge do I want to use?
A) .22 Long Rifle so as to be usable at Appleseed and Rimfire Challenge events.

Q) Precision and/or accuracy requirements?
A) 4 MOA precision or better.

         Given these conditions, I set to work researching what was out there. Spent time browsing internet forums looking at what was being used by like-minded people. I quickly learned that AR-type rifles chambered for .22LR - I'll just call them AR22's - are made by Smith & Wesson, Mossberg, Tippmann Arms, CMMG, Tactical Solutions, Palmetto State Armory, 2A Armament, Colt, Compass Lake Engineering, and probably more. The Smith & Wesson M&P15-22 and the Mossberg 715 seem to be the most commonly seen models online, at gun shows, and at the ranges. Project Appleseed has prohibited the M&P15-22 for the foreseeable future, so that's not an option. [Editor's Note: The Smith and Wesson M&P 15-22 is now allowed at Project Appleseed events, but the shooter must have their bolt gauged on site and fill out a special waiver]

         After researching for a while, imagining what I'd like for myself and looking at what other people are using, I settled on some constraints. My rifle build would adhere to the following criteria:

  • A2 furniture (pistol grip, buttstock, handguards)
  • A4 iron sights (fixed front sight base with detachable carry handle rear sight)
  • Rifle-length configuration (sight radius and handguards)
  • 16" barrel, for the "dissipator" look (call me quirky, but I've always had a thing for the dissipator configuration)
  • Free-floated barrel (for enhanced precision)
  • A nice trigger (because I'm snobby about triggers)
  • Reliable, safe bolt and bolt carrier design (so as to be immune to any foreseeable Appleseed Oversight Committee prohibitions in the future)
         It would be a free-floated dissipator in .22LR:

         Right away, this presented at least one major problem: a 16" barrel chambered specifically for .22 Long Rifle with a gas block journal at the rifle-length position. All my hours of research found absolutely nobody - and I mean nobody - who offered a product which met these criteria.
         At this point, I had three options available: (1) buy a 16" barrel blank and have it custom machined to fit my criteria, (2) buy a bunch of separate parts and assemble it myself, or (3) change my mind about some of the criteria and go another route altogether.
         What I did was a combination of options 2 and 3. I changed my mind on the 16" constraint, and adopted a 20" constraint. That way, finding an appropriate barrel would be much easier, and I could always take it to a machinist later on to be cut down to 16" if I really wanted to. (It seems to me that the optimal barrel length for .22 Long Rifle is 16" or 17", and this was convenient for my coincidental fondness of 16" AR barrels. As the barrel length increases beyond that, the general pattern appears to be that muzzle velocity decreases but precision improves. There must be a point of diminishing returns where you also begin to lose the precision benefit, but I don't know where that point is. I have a Ruger 10/22 with a 22" barrel, and it shoots very well, so I'm comfortable going with a 20" barrel on this project.)

         So, my modified criteria for the build project became:

  • A2 furniture
  • A4 iron sights
  • Rifle-length configuration
  • 20" long, free-floated barrel
  • Nice trigger
  • Safe and reliable
         This is a much more user-friendly set of criteria. It'll basically be a Service Rifle in .22 Long Rifle.

Part 2/5 : Part Selections and Reasoning
Lower Receiver. Aero Precision forged stripped lower receiver.
I discovered Aero Precision in.. I think it was 2013.. and they have become my default choice for receivers in my AR builds, because they're good quality and they're unimposing. Heaven forbid I find myself in the absolute worst place, at the absolute worst time, and have to use a rifle in self-defense, and my rifle ends up in the evidence locker. In such an event, I don't want that rifle to cast me in a "wannabe vigilante" light. The word "tactical" isn't in their company name, it's not stamped anywhere on the receiver, there's no menacing logo, no gung-ho safety markings, no aggressive styling to the machining, nothing like that for a prosecutor to use against me. (They're still going to do their job, but I don't want to make it any easier for them.) I wish I didn't have to think that way, but that's the world we live in nowadays. Plus, they're high-quality receivers, they're affordable (and can often be found at even better sale prices), and they're made in the generally gun-friendly State of Washington. Aero Precision receivers get the official Willociraptor Stamp of Approval.

Lower Parts Kit. With lower parts kits ("LPK's"), generally speaking, parts are parts are parts. I've built rifles with LPK's from a variety of manufacturers, and I can't tell the difference - but my wallet sure can. The only parts that I approach with an eye for construction are the hammer, trigger, and disconnector - collectively referred to as the fire control group ("FCG"). I picked a CMMG partial LPK (FCG and pistol grip not included), because that's what was available at my local gun store.

FCG. I went through a phase of wanting to get into NRA Service Rifle shooting, and I picked up a Rock River Arms 2-stage chromed National Match trigger a while back. I like it a lot. It's got a good reputation, has a nice clean break, physically feels good on my finger, is light but not too light (still heavy enough for use at Camp Perry), and - at least insofar as National Match triggers typically go - also affordable.

Furniture. I already have a full set of matching green Rock River Arms A2 furniture (pistol grip, buttstock, and handguards) on-hand. This was a no-brainer decision. I like green furniture on my AR's, because it makes them shoot better!  ;-)
Grip -

Stock -

*NOTE* I added a Rock River 3.5lb lead weight to the stock just for good measure. I like hefty rifles, and I prefer back-heavy over front-heavy. (Spoiler alert: this rifle ended up with an unloaded weight of 12lb 1oz.)  >:D

Upper Receiver. My local gun store has Anderson Manufacturing stripped upper receivers at good prices, so that's what I picked. I filled it out with an upper parts kit and delta pack from LBE Unlimited, which were affordable and available at the gun store.

Barrel. I chose the CMMG 20" rimfire barrel kit, because the barrel has the government-style profile that uses rifle-length handguards and front sight block (FSB). It came with a bolt carrier group (BCG), so I saved a good chunk of money compared to buying the barrel assembly and BCG separately. Plus, had I gone that route, I may have run into problems with the CMMG FSB not fitting the float tube quite right.

Bolt Carrier Group. One CMMG "Arc22" rimfire BCG was included in the barrel kit.

Charging Handle. I picked the CMMG rimfire charging handle to ensure proper function with the rimfire BCG. Turns out any old charging handle will function just fine, though.

Float Tube. Float tubes for Service Rifles are offered by Rock River Arms, Fulton Armory, White Oak, Compass Lake Engineering, and probably more. I selected the CLE float tube kit for their method of welding the sling swivel mount onto the tube - they're the only ones I found who do it that way.

Handguards. I originally intended to use my green Rock River Arms A2 handguards on this build, but upon receiving the CLE milspec composite handguards (which came with the float tube kit), I quickly noticed the superiority of the CLE handguards over my Rock River handguards. So I just painted the green grip, the green stock, and the black handguards all the same shade of Rustoleum camouflage Deep Forest Green, with a coat of matte clear. Now they all match.

FSB. I picked the CLE forged "F"-marked preban adjustable front sight block. In case there was anything proprietary going on with their float tube, I wanted to have a FSB that would fit. CLE float tube, therefore CLE FSB.

*NOTE* This part came with a NM front sight post measuring 0.052" across, and tapered. It's so pretty I made it my profile avatar!

Muzzle Device. In the KISS spirit, I'm just going with a plain-old vanilla A2 "birdcage" flash hider. They're still legal where I live.. for now.

Rear Sight. I have had an Stag Arms detachable carry handle rear sight sitting around for quite some time now. I used it on my centerfire AR to shoot score at a Known Distance Appleseed. Easy choice to use this part on my build project. Having a detachable rear sight allows me to use a scope if I want to.

Sling. The list of slings that are better than the good-old USGI web sling is a very short list. The list of better slings at better prices doesn't even exist…. So that's an easy decision to make.

**NOTE** For you investigative types, you'll notice the MSRP's on these parts adds up. It's totally doable to get these parts for much less elsewhere. I did it, and so can you!

Part 3/5 - Assembly
         Assembly happened in a couple of different sessions: lower receiver assembly, upper receiver assembly, and barrel installation.
         Assembling the lower receiver was simple enough. I've done this a few times by now. I'm not going to walk readers through how to do this, because there are gazillions of other tutorials out there. (Same for assembling the upper receiver.) My project sat like this in limbo, with just the complete lower half and assembled upper receiver, for a very long time, as funds kept needing to be used on other things.
         The day finally came when I had enough money squirreled away to finish the project, so I ordered everything all on the same day. After everything was delivered, I had all that I needed to put it together. I've assembled many lower halves, but this was going to be the first time I'd ever just taken a bunch of parts and assembled them into a complete upper half.
         I learned that my armorer's wrench didn't fit around the float tube and therefore couldn't be used to tighten the barrel nut. I went to my local gun store to talk to them about my problem, and they kindly allowed me to borrow one of their barrel nut wrenches to complete my build. But their wrench didn't fit around the float tube either! They took it into the back of the shop and gave it a few rasps with a file until it did fit, then re-blued the newly exposed metal. We shook hands and I thanked him, and then I went home to install everything.
         Arranged everything and got to work. Cranked it to 30 ftlbs to start with, then 40.. 50.. 55.. 60.. 65.. 66.. 67.. and finally 68 ftlbs of force on the barrel nut before it was properly timed to accept the gas tube. (I know, the gas tube is completely unnecessary for an AR22, but I wanted it there!)
         There was a snag that I kept hitting while installing the float tube which I would now like to address. Before torquing down the barrel nut, I would align the gas tube slot in the float tube's 12:00 position with the barrel's 12:00 position, and then torque it down. The float tube would invariably rotate very slightly at the last possible moment, and the gas tube slot would be misaligned with the slots on the barrel nut. I must have repeated this process four of five times, before I tried something different. I measured the distance it had rotated, loosened the barrel nut, realigned the float tube, and rotated the float tube in the opposite direction for the measured distance it had traveled before. It worked like a charm. The next time I cranked everything down and the float tube rotated at the very last possible moment, it landed exactly where I wanted it to be.
         Next up was the FSB installation and alignment. Installing it was as simple as sliding it over the barrel and into place on the gas journal. I left a business card's worth of space between the FSB and the handguard cap so as not to adversely affect the free-float I wanted.
         Aligning the FSB was a little trickier than installing it, but I had an idea. My kitchen countertops are granite and are very flat, so I simply installed the carry handle rear sight, set the rifle upside-down on my kitchen counter and fiddled with the FSB until all four tips were touching the granite. Tightened down the set screws, and voila!

         Sidenote: I called Compass Lake Engineering directly to ask how much torque to apply to the FSB's set screws, and was told to simply tighten them to whatever I could get out of a short-head allen wrench. I was surprised by the vague nature of this response, but a short-head allen wrench generally tops out at about 20-25 inlbs before something either slips or strips. So even though it's a vague response, it's still useful. I tightened all four set screws to 25 inlbs using a Wheeler FAT Wrench and the FSB feels pretty solid. Installed the flash hider, and the upper half was functionally complete.

         I painted the grip, stock, and handguards all the same color green, and poof. Done.

         Final assembly complete!   :F

Part 4/5 : Performance
         The rifle was test-fired two days after assembly, using ten rounds of CCI Mini-Mag Round Nose ammo, in two sets of five rounds. Nothing blew up, so, you know, that's a plus.
         The iron sights were set to mechanical zero, and a "Squares" target was shot at 25m. Holes were on paper, so that was good. Apparently my low-tech stunt with the kitchen counters worked fairly well, because even though my elevation needed dramatic correction, necessary windage adjustments were much less. The second group was acceptable, especially for a simple test-firing session. After all, I was going more for function checks than precision assessment. None of that until I at least identify what kind of ammo it shoots best from a rest.

         The next weekend, I got to spend some time with a friend who knows a whole lot more than me about AR's in general, including AR22's. We talked about how his build turned out and what obstacles he'd hit along the way, and he recommended that I do some polishing to the BCG and showed me where.

         The weekend after that, I got to take it to the range and do some intensive ammo testing. I had to do my testing at 50 yards, because the 25yd line on their pistol range was buried from a recent landslide due to all the rain we've been getting recently.
         I tested the following ammunition through the rifle:
  • Aguila 20gr Colibri
  • Aguila 20gr Super Colibri
  • Aguila 40gr SuperExtra High Velocity RN
  • Aguila 60gr Sniper Subsonic RN
  • CCI 40gr Standard Velocity RN
  • CCI 40gr Mini-Mag RN
  • CCI 36gr Mini-Mag HP
  • Federal 36gr "Redbox" bulk HP
  • Federal 36gr "Bluebox" bulk HP
  • Federal 40gr AutoMatch bulk RN
  • Federal 38gr American Eagle HP
  • Federal 38gr GameShok RN
  • Federal Premium 40gr Gold Medal Target RN
  • Federal Premium 40gr Gold Medal HV Match RN
  • Fiocchi 40gr Standard Velocity RN
  • Geco 40gr Semi-Auto RN
  • Remington 36gr Golden Bullet HP
  • RWS 40gr Target Rifle RN
  • Winchester 36gr "Whitebox" bulk HP
  • Winchester 40gr Super-X Super Speed RN

         I won't bother posting all the raw data from my experiment, but the best performers were CCI 36gr MiniMag HP (1-2 MOA), with the 40gr MiniMag RN's in second (2-3 MOA). The CCI 40gr Standard Velocity RN (3 MOA) and Fiocchi 40gr Standard Velocity RN (3-4 MOA) also performed very well. This is all including human error - no shooting rest involved, just a shooter, a rifle, and a sling - so they probably perform even better than that from a rest. For the type of shooting I'll be doing with this rifle, the difference is practically negligible.
         Counting all five rounds in that group, the maximum spread was 0.883", which is 1.686 MOA at 50yds. Average distance to center of group = 0.343" (0.655 MOA).

         If you dismiss the flier and only count four rounds, the group looks MUCH better. Max spread of 0.563" (1.075 MOA), average distance to center = 0.278" (0.532 MOA).

         Shooting this rifle just makes me smile. It looks and feels like a for-real AR (and I guess it is).... but when you shoot it, you realize that you're holding something special. Recoil is negligible; the power of a .22LR round doesn't hold a candle to the rifle's inertia. In standing, the sights just do a tiny little dance and you're back on target. In any other position, the sights barely move at all. I'd love to see what Jerry Miculek could do with one of these!

         A rainstorm came pretty abruptly to the range, and the Range Officers didn't let the shooters go downrange to switch out their targets when the line went cold again. Kinda silly if you ask me, but hey, their range their rules. My target fell off of its staples almost immediately after the range went hot again, so my precision testing was clearly over with since I had no target to learn from. Loaded up a couple of magazines and let my friends just shoot it at the berm. Everybody who shot it loved it. Lightning came and the RO's closed the range, so we packed up and left. (Of course, just as everybody was leaving, the skies cleared up just as quickly as they had darkened. Typical.)
         The best group came from CCI 36gr MiniMag HP's. It's tempting to make this my primary ammo type to stock up on for use in this rifle, but I think I'll go with the CCI 40gr Standard Velocity RN's. The MiniMags start out supersonic and quickly go subsonic, destabilizing and losing most of their accuracy in between while crossing the "transonic zone." The Standards are subsonic to begin with, so they do not cross any transonic zone. While the MiniMags show (marginally) better results at 50yds over the Standards, the Standards will retain that marginally-lesser performance much better than the MiniMags. I'm not sure at what range the transonic turbulence becomes an issue for 22LR rounds - in all reality, it's probably further than the ranges at which this rifle will do 99% of its shooting - but I'll play it safe and go with the Standards. Which is convenient, since my other rimfire rifle likes CCI Standards as well and I only have to stock up on one type of ammo.
         So that's that. First actual range trip for the new AR22. I'm very happy with how the build came out, and look forward to shooting it at future Appleseed and Rimfire Challenge events. I now have a rifle that fits all of my project criteria and builds AR15-compatible muscle memory for cheap. Mission accomplished!

         PS - I checked my ballistics calculator, and the MiniMag HP's go transonic at 41yds. This is interesting, since they grouped very nicely at 50yds. Still gonna stick with the Standards, though.

Part 5/5 : Lessons Learned

1.       Granite countertops are pretty flat.

2.       Barreling a rifle isn't rocket science or voodoo magic, like I thought it was. (At least for a rimfire. I still think that, for centerfire builds, headspacing the barrel and bolt are better left to professional gunsmiths. And I am not a gunsmith.)

3.       Certain parts marketed as rimfire-specific need not be purchased. For example, the I spent money on the CMMG rimfire charging handle when one of my spares would have provided the exact same function. You can even use one of your fancy charging handles with special latches - or ambidextrous functionality or what have you - with the CMMG BCG and it'll work just fine.

4.       (Not my idea - read it on the forums at Since 22LR's are more prone to misfires/jams/etc, you may benefit from wrapping a ziptie around the latch on your charging handle. It will keep the latch unhooked from its corresponding recess on the upper receiver. That way, if/when something doesn't go right, you can simply use your trigger hand to rack the bolt. No need to un-sling your support arm. I dismissed this idea at first, but after a little bit of range time, I'm a believer and a convert. If you have an ambidextrous charging handle, the ziptie isn't necessary, just use it the way it was designed.

5.       As it stands at the time of writing, this rifle does not have a bolt hold-open feature. The bolt will hold open when the last round is fired from the magazine, but once you remove the magazine from the rifle, the bolt goes forward. I would do well to figure out a solution to this problem. There are two solutions that I know of:
         (a) The Better Mag Adapter, made by Redi-Mag, is a gadget that you insert into your magazine well, and use with S&W M&P15-22 magazines. It functions as a "spacer" between the magazine and the BCG, and has a sort of built-in "lip" on which the BCG catches when the magazine is empty. The bolt locks back on the last round, and stays back when you remove the magazine.
         (b) The "Catch22" bolt catch, which entirely replaces the normal bolt catch in your lower receiver. This means that your lower receiver will be "dedicated" to 22LR use. (At least until you swap it back out.) It's just like any other bolt catch, but with the aforementioned "lip" integrated into the design. It catches the BCG when the last round is fired, and the bolt stays back when you remove the magazine.

6.       All the magazines that are currently made to be used with the CMMG system are long-format magazines. That is, they all resemble 30rd magazines - regardless of their capacity. Both 25rd magazines and the 10rd magazines have the same exterior dimensions. This could lead to some confusion, so make sure to mark them somehow. Also, these long-format magazines may interfere with your support arm when you're in position. There are some short-format CMMG magazines out there, but as far as I know, they're no longer made.

7.       Considering items #5 and #6 together, I'd personally recommend NOT stocking up on CMMG magazines, and using the S&W magazines instead. They're more reliable than the CMMG's, easier to use than the CMMG's, more readily available than the CMMG's, can be used with the Redi-Mag BMA (which doesn't require modifying your lower half), and come in both long- and short-format dimensions (to not get in your way while in position).

8.       A 12lb AR22 might be a little on the heavy side for some, but I contend that you'll be too busy smiling to notice!