Everything you never wanted to know about CMMG ARC-22 conversion

[dbeardslee]

So I ordered some new toys - a CMMG ARC-22 and some accessories - and I learned a few things in the process. If you're considering adding the 22 conversion to your AR 15, here's some things you might want to know.

First, the ARC-22 comes in several different flavors...

The base model is the Alpha. It comes with bolt hold open magazine(s), and has a one piece machined chamber insert, and can be had in a parkerized finish. The bolt hold open magazines hold the bolt open on the last shot, but allow the bolt to go forward as soon as you remove the mag. The mags require some minor sanding on two tabs on the back, and to me that's a good thing - it insures a nice snug fit. MSRP $189.95



The next rung up in the ARC-22 line is the Bravo model. The Bravo is stainless steel, and uses a removable brass bushing on the chamber insert. It also ships with the bolt hold open magazines. MSRP $219.95



One more notch up the price scale brings us to the Echo model. This kit adds the anti-jam charging handle, and forward assist adapter. MSRP $269.95



Which brings us to the Cadillac - the India kit. This kit adds the bolt hold open adapter (BHOA), a magazine loader, and the big one - a locking brass chamber lug that keeps the assembly from budging once installed. MSRP $319.95



And here's what I decided to do. One of my main reasons for buying the kit was to add 22lr capability to my AR at a reasonable price. I ordered a Bravo kit with three bolt hold open magazines. Shipped to me price was $214.30. But like every other firearm related thing I buy, I couldn't leave it alone. Had to add some accessories and functionality.

First addition was a BHOA. The BHOA is made out of polymer with a steel insert, and it allows your bolt release to function the same as it does when shooting 5.56. Shipped to me price was $21.89



For the BHOA device to work properly, magazines need to have BHOA followers and springs. The tip of the follower is spring loaded so it will move to the back when the last round ejects, catching the tab on the BHOA and holding the bolt to the rear. So I ordered three BHOA followers and springs at a shipped to me price of $25.21.



As I got reading up on these things the one thing I was seeing consistently was how dirty these conversions get. I think part of that is due to DI guns dumping nasty 22 lr discharge back into the receiver via the gas tube, and part may be due to gasses escaping around the insert and coming in through the chamber. I'm not worried about carbon being injected by the gas tube as my AR is piston driven (the kits work with piston driven rifles without the need to remove the piston, but you do need to shut off the gas). In order to keep any fouling coming out of the chamber to a minimum, I thought the locking lug would be a good addition. The locking lug replaces the smooth brass bushing on the Bravo model. You slide it in, and manually move the catch to the center from the bottom of the upper. The BHOA has a notch that the lever fits into so that it cannot rotate back out after installation. Locking lug shipped to me price was 29.70.



That brought my total expenditure to $291.60. You might think it would have been more cost effective to just bite the bullet on the India kit, but remember that the MSRP of $319.95 only includes one magazine, and the BHOA mags run about $25 ea. The forward assist adapter is kind of interesting, but hardly necessary for 22 lr. I'm not about to start banging on a forward assist to try and force a 22 into a chamber. It's nice with 5.56, but with 22 lr I'm thinkin' I'm better off without it. I also didn't see a need for a dedicated charging handle as the stock unit works fine. The dedicated charging handle creates a tighter fit with the top of the conversion and it's supposed to eliminate certain types of jams.

I'm expecting to have to do some fitting on the BHOA followers to get them to work smoothly, but I'll have to wait until they arrive before I'll know for sure. I'm going to wait until I've got all the parts installed before I take her to the range for a test run. In the mean time, I've got all this stuff and needed someplace to keep it. Another $17 got me a brand new East German surplus 4-mag pouch that works perfect. The mags take up three of the slots, and the BHOA and ARC-22 fit in the other pocket. Pretty sweet. Sweet enough that I'm going to order some more for my AR 15 magazines. Nice pouch - Unissued East German surplus 4 mag pouch

I'm sure some folks are going to say that it's nearly as cheap to just buy a dedicated 22, but I'll have to disagree strongly with that. You could buy the rifle, but when you consider optics, triggers, and the like it winds up being a lot more expensive - at least in my case. I can still use my existing flip up irons, red dot or 4-12X40, and my 3.5lb trigger goes along for the ride too. Not to mention hand guards, pistol grip, and trigger guard. To me this seems like a cost effective way to go, and the rifle has the same controls and goodies that were so painstakingly added to my AR.

Anyway, if you've been thinking about one of these conversions, that's the latest poop from group. I hope you find it helpful - or at least interesting.

[Zylo_X]

Outstanding info! Thanks for posting. I've toyed with the idea of a dedicated 22 or 22 conversion, but just never pulled the trigger. I'll probably not get back to it for awhile, but good points to consider. Truth be told, for as little trigger time as I really get with the Colt, 'cheap' .223 is fine for now, but like you said, we gotta accessorize. Looking forward to the final range report, and more pics, of course.

[Lmstncwby]

Cool! Nice summary! I had heard you need to used the Echo or India with the Ruger SR556 piston gun due to stroke length. Anyone know about that?

[dbeardslee]

Cool! Nice summary! I had heard you need to used the Echo or India with the Ruger SR556 piston gun due to stroke length. Anyone know about that?

Near as I can tell there isn't any difference in the location of the recoil spring housing on top of the conversion between any of the CMMG units. Evidently they moved it back a tad from the original design to accommodate piston guns. I dropped a bravo unit in my Stag model 8 with no need to futz with the piston rod, and the rod protrudes into the upper receiver 1 3/8 inches. I'd be willing to bet the Ruger's comes back into the upper about the same distance since the bolt carrier key should be in the same place on the carrier. You might try measuring just to make sure.

It's blow back operated so you don't actually use the gas system nor a piston, so the stroke length should be irrelevant. What's important is how far back into the receiver the rod protrudes. You'll need to shut off the gas though, so the piston is just going along for the ride. I think a piston gun will actually work better with these units than a DI gun. I read a number of reports of 22lr plugging up the gas tube on DI guns, but they also said running five or six 223's through afterwards would clear the blockage due to the 223's significantly higher pressures. And of course you won't be getting all the crud blowing back into your upper - just what can escape around the chamber insert bushing.

Truth be told, for as little trigger time as I really get with the Colt, 'cheap' .223 is fine for now, but like you said, we gotta accessorize.

That's one of the reasons I bought this thing. The rifle range is only open three days a week at the gun club I belong to, but I can shoot it with the conversion on the 25 yard plinking range and the 50 yard pistol range - and for about one tenth the cost.

And one last thing I failed to mention in the original post. You can save a few bucks on the parkerized version, but I don't think it's worth the savings. Evidently the rough parkerized finish causes some problems with the bolts operation, and the fix is to remove it where the bolt and rails mate. You don't have to worry about it with stainless steel, and from what I can tell the bravo, echo, and india units are only available in stainless.

[RevolverFan]

Wow, excellent! If I had an AR, I would have to get a conversion kit!

[dbeardslee]

Here's a little more info for the SR556.

This is a shot of the inside of the upper on an SR556. Note how far into the upper the operating rod protrudes -



And here's a shot of the inside of the upper on my model 8. Looks like the operating rod protrudes about the same distance as the Ruger's -

[dbeardslee]

The BHOA followers arrived today, and I got the first one installed and functioning. I learned a few things in the process too. First, the spring that comes with the follower isn't bent properly where it mates with the follower. The loop that the leg of the follower goes through is a little too far away from the coils, and I had to shorten the distance a bit. The follower itself is a bit on the portly side. I had to narrow it a bit with a file, and I also took the mag apart and did some smoothing in the follower channels (you need a 3/32 allen wrench to disassemble the mag) and gave the inside a shot of Rem Dri Lube. I got it where the follower goes up and down okay, but the spring didn't have enough 'oomph' to activate the BHOA.

And that's when I had an epiphany. You need to use both the stock spring as well as the BHOA spring for it to work properly. I didn't wrap the stock spring around the leg of the follower as I had read about the stockers being too fat for the BHOA follower. I just put it in the channel and slid it up under the follower, and it made the difference. That gives enough spring tension to activate the BHOA. I could only get fifteen rounds in the mags, but the manual pretty much tells you that it takes a while before you can load the full 25, and recommends only loading 15-20 until they break in. I'll give the springs a while to settle down and see what happens.

The other thing you have to do is adjust the BHOA. It comes with a long thin allen wrench to do the job, and you can access the adjustment screw through the mag well. It's a pretty fine adjustment - too far in and the bolt will hold open every time. Too far out and the BHOA won't work. 1/2 a turn made the difference between working and not working, and I just had to play with it a bit to get it right.

I loaded the mag with fifteen rounds, and cycled them through. They all fed fine in hand cycling, and the bolt stayed to the rear after the last round was ejected. I dropped the mag and the bolt stayed to the rear, but a tap on the ping-pong paddle sent it back forward. Exactly the way it's supposed to work. So far so good.

For right now I'm just going to install one BHOA follower, and I'll run the bolt hold open followers on the other two for the sake of comparison. As soon as the locking lug comes in I'm off to the range to do some live fire testing.

[dbeardslee]

I know I said I wasn't going to screw with the other two magazines until I got to the range, but anyone who knows me should have known that was BS. I just finished the other two mags, and in the process came up with what I believe to be the definitive way to install the BHOA followers in the mags. So sit back gentle readers, and let me show you how it's done...

First you need to understand what causes the problems with the followers. It's less the follower causing the problem than the spring itself. Note in the following picture how the loop on the spring sticks out a bit in front, and the coils stick out a bit in the rear. I believe this to be the primary cause of the followers sticking in the channel.





And here's my fix. It's quick, easy, and it works. First you need to drill a very small hole in the leg of the follower. Don't drill the hole all the way through the leg of the follower - 2/3rd's of the way into it is plenty. The hole is clearly visible in this pic...



Next you need to do a little filing on the flat sides of the follower. There are two roll pins that hold the spring-loaded assembly in place, and they tend to stick out a bit. The pins need to be flush with the sides of the follower, and the follwer needs to be a tiny bit thinner to run smoothly in the channel. Then clip the end off the spring such that you just have a straight piece of wire sticking out past the coils...



Stick the clipped end into the hole. Once it's inside the follower channel it's impossible for it to come back out. You can see clearly in the pic how this mod gets the spring completely under the follower, and there's no loop to catch on the front.



You'll probably need to do some minor smoothing on the mag channel itself as there are several raised dots left over from the mold, and they need to go away. Spray the channel halves with a little Rem DriLube, and reassemble, but leave the screws a little loose. Insert the follower far enough to get the spring loaded top started but leave the hole exposed, put the spring in the hole and get it started, and then add the factory spring in the round hole. Push both springs all the way into place at the same time, put the floor plate back in, tighten the screws and you're ready to go.

I think this is the easiest way to install the followers. It's quick, and requires pretty minimal modification compared to some other techniques I've read about. And it works. I can feel how smoothly the followers go up and down inside the mags using a wooden dowel to compress it, and they're easier to load too.

[dbeardslee]

And here's another option. As I get looking at the documentation on CMMG's site, I see that I had the spring in upside down. Probably works a lot better in its proper orientation. However I will say this - you're still likely to need both the factory spring and the BHOA spring to get the unit to work properly. Even when the follower is running very smoothly with no dragging, the BHOA spring just isn't strong enough to overcome the AR15's bolt hold open spring. But with both springs installed it works pretty good. So I'm going to revise my recommendation on doing the upgrade to only smoothing the sides of the followers and the insides of the mag channels, and using both springs - preferably in their proper orientation.

[dbeardslee]

The locking lug came in, and I got it installed. It was a little bit tricky, and you need a small pair of snap ring pliers and a piece of 3/8" tubing to do it. The snap ring is tiny, and under it there's a plastic threaded locking ring that fits into a recess in the lug. I used the tubing to slip over the chamber adapter and was able to tighten the ring by using a little pressure on the tubing while turning it - if that makes any sense. Anyway it worked, and the locking lug does exactly what it's supposed to.

I've also found that loading the magazines is a bit hard on the finger, so I went ahead and purchased a CMMG mag loading tool. It's nothing fancy - just a piece of stamped steel bent to the appropriate dimensions. It allowed me to load 25 rounds in magazines with the BHOA follower installed, and 27 rounds in a mag with the bolt hold open followers. It takes a lot of pressure to load 25 in a BHOA mag, and I dimpled a couple 22lr's that way. In looking at the design, the part of the loader that contacts the round was straight cut, which meant that it only made contact with the casings at a tangent. To solve the problem and allow using a little more force without damaging the rounds, I radiused the 'contact piece' with my dremel tool. That spread out the forces enough (due to more contact with the casing) and the dimpling stopped. I don't think I'll actually load 25, but it's nice to know I can if I want to. I also used a little of the handyman's secret weapon around the outside of the tool. It's only bent, and there are no welds on the unit so I used duct tape to hold it together a bit. Here's what it looks like.



And you can see the readius on the tip of the contact piece in this pic...



So I've got all my goodies together, and tomorrow I've got someone to watch mom and what looks like it will be a good day for shooting. If all goes as planned I'll get to the range tomorrow for some live fire testing.