The Unforgiving Minute

What I wanted, why I wanted it, how I decided to get there.

When I finally decided to go down the AR road, I made a conscious choice to go for the lightest reasonable weight possible without resorting to exotica like special lightweight aluminum bolt carriers or other racegun parts. Basically, I wanted a light, handy carbine, a modern descendant of the M1 carbine of the WWII era. I specifically did NOT want to go the way of so many modern M4geries, covered in yards of Picatinny rail and accessories of dubious value, and mashing the scales at 8 lbs or more. I wanted to come in a lot closer to the M1 carbine’s feathery 5.2 lbs.

With that in mind, the Cavalry Arms Mk. II lower was the natural choice. A single piece of polymer (vibration-welded together from two injection-molded halves) forms the complete lower receiver/buttstock/pistol grip assembly. This saves a full pound over the weight of a complete A2-style lower, or about a half-pound over the weight of a lower with an M4-style stock.

When I heard that Cavalry Arms, after a long-running dispute with the BATFE, was surrendering their FFL and ending production of lowers, I rushed to grab a black stripped lower while they were still available.

There are a few quirks to building on the Cav lower (covered later in this post), but a regular, off-the-shelf AR lower parts kit basically drops right in. My lower parts kit is from DPMS and is entirely unremarkable; it’s the same kit you can get anywhere for about $60.

The upper needed a bit more thought. I knew I wanted a 16″ barrel, but researching and talking to serious AR geeks led me to go for a midlength gas system, rather than the more common carbine length. Compared to the carbine length gas system, a midlength has significantly lower pressure at the gas port and a shorter dwell time (the time between the bullet passing the gas port and leaving the barrel), both of which contribute to smoother cycling, easier extraction, and less wear and tear on the action.

The gas system advantages of the midlength are its greatest strength, but it also offers a few other benefits. Sight radius is extended a bit by moving the front sight closer to the muzzle. The longer handguard and shorter length of bare barrel just plain looks better to my eye. And yes, unlike a standard 16″ upper, you can put a regular M16/M4 bayonet on a middy. On the down side, it will weigh a tiny bit more than a carbine-length gas system upper, due to the longer gas tube and handguards. I figured the benefits outweighed that slight disadvantage.

Keeping with the “minimum practical weight” plan, I wanted a lightweight contour barrel. Midlength uppers are readily available, if not nearly as popular as carbine-length uppers. Lighweight midlength uppers are not so common. CMMG offered such uppers for a time, but production was discontinued by the time I found out about them. Rock River Arms builds a lightweight midlength, and I planned to get one until I found out about Bravo Company’s version.

The difference? Bravo uses 1:7″ twist barrels (vs. 1:9″ for RRA), M4 feedramps, taper pins on the front sight base, and barrels and bolts that have all been subjected to magnetic particle inspection and proof firing. Basically, Bravo builds to USGI standards, the fact that the military doesn’t use midlength uppers notwithstanding. The RRA upper would probably have worked out just fine, but I was willing to spend a few extra bucks for the Bravo Company upper. Evidently a lot of other people had the same idea, because this batch of uppers sold out in about a day and a half.

Bravo’s lightweight contour is light under the handguards, flares up to the standard .750″ for the front sight base, and is lathed down to about .580″ between the front sight base and flash hider. More weight could have been saved by using an M16A1-style .625″ front sight base, but those are not easy to find anymore. As it is, turning a quarter-pound off the muzzle end does very nice things for balance and handling.

Putting It All Together

I’m not going to write a how-to on assembling an AR lower; the internet is awash in guides, and really the process just isn’t that hard. If you’ve detail-stripped a few guns and gotten them back together successfully, you can certainly build out an AR lower. I do recommend this guide at ar15.com, along with Stingray’s addenda and the Brownell’s assembly videos.

That said, the CAV-15 lower throws you a few quirks, and I’ll share with you some information I wish I’d had before I started.

A regular AR-15 lower uses the threaded-in buffer tube to hold the buffer retainer captive in its recess. Since the Cav lower lacks a separate buffer tube, it instead uses a transverse roll pin for this purpose. There’s a pre-drilled hole for the pin, but the hole in my lower was poorly drilled and a bit undersize. I carefully chased it with a 5/64″ drill bit, then chased the buffer retainer hole to clear out the plastic shavings.

Now, start the roll pin in its hole, use one hand to compress the buffer retainer and spring into their recess with a pin punch, hold the roll pin punch with your other hand, and use your third hand to tap the roll pin into place. And now you see the problem. You’ll either need an assistant or some kind of dowel or other object to keep the buffer retainer compressed while you tap the crosspin in place. I did not have an assistant on hand. It was a lot of fun.

The other quirk on the CAV-15 is the installation of the selector detent and spring. On a regular AR, these parts are installed from below the receiver and retained by the pistol grip. The Cav’s integral pistol grip makes this impossible. Instead, you have to install the spring and detent from the top, then compress them into place while installing the selector.

Bear in mind you are going to have a very tiny, very pointy piece of metal pointing straight up under heavy spring tension. If you slip, that very tiny, very pointy piece of metal will either embed itself in your ceiling or attain low earth orbit. Decide now whether you would rather laugh or cry when this happens.

The right way to deal with this is a slave punch. Use one small-diameter punch to (CAREFULLY!) compress the selector detent down into its hole, then stick a fat punch in from the right side of the selector hole to capture the detent. When you push the selector into place, it will push the slave pin out and you’ll keep the detent safely captive within the gun. Bask in your clever, tool-using superiority.

The rest of the lower build was uneventful and unremarkable. I did have to slightly open up the bolt catch recess and the gap between the pivot pin lugs on the front of the receiver. The pivot pin boss on my upper was a flat .500″ across, with the gap between the lugs measuring just a few thousandths less. I very slowly, very carefully opened up that gap just enough for a snug fit. Could I have simply forced the parts together? Probably, but that would put a lot of stress on the weld seam at the front of the magazine well, and I really have very little interest in ruining a brand-new, no-longer-made lower receiver!

With everything put together, the gun tips the scales at 5.75 lbs according to my dubious little food scale. I’ll ask the guys at the gun shop to drop it on their postal scale to get an exact number. Not quite the 5.2 lbs of an M1 carbine, but close enough to make me happy. It also balances and handles REALLY nicely.

Bits ‘n’ Pieces

I debated about rear sights for a good while. A regular removable carry handle was my first idea, but they’re actually fairly heavy and I doubted I’d ever use the handle. I eyed the Daniel Defense A1.5 rear sight pretty hard and ALMOST pulled the trigger on ordering one. Then I finally decided that, while there are no immediate plans for an optic, I really ought to get a folding rear sight just in case I eventually want to mount a scope or red dot. I went with the Bravo Company-branded Troy Battle Sight. It’s a pretty simple folding unit with a same-plane aperture and adjustment only for windage; elevation is adjusted at the front sight. Given that I doubt I’ll ever shoot this gun much past 100 yards, I’m not concerned about the lack of elevation adjustment at the rear sight. I did degrease the threads and add a drop of Loctite before screwing it down tight.

My first batch of magazines consists of six aluminum 30-rounders and two aluminum 20-rounders (for bench and prone shooting), all from C-Products. CDNN has good prices on these; $8 for the 30s and $10 for the 20s. I know all the cool kids are running Pmags these days, and I might eventually order a few to try. These ought to work just fine as long as they don’t get stomped or stored loaded for too long.

Finally, I got the Brownell’s/CMMG .22 conversion kit. This is just the latest version of the old Atchisson-style conversion bolt paired up with some Black Dog Machine 27-round magazines. Should make for fun low-cost plinking and teaching new shooters. I’m told that the Aguila Sniper Subsonic round does really well in fast-twist barrels, since it’s basically a long 60-grain bullet loaded in a .22 Short case. I’m going to order a box or two and see how they work out.

Completing the Package

The final piece of the puzzle came to me as a birthday present from my indulgent and long-suffering girlfriend: she gave me a set of Cavalry Arms C8 midlength handguards and helped me snap them into place. With the rifle complete, she hit me with an unexpected question: “What’s her name?”

I’ve never named guns before. Never even thought about it. So I gave my loving girlfriend the honor of bestowing a name. Her immediate answer: Vera.

Then I pointed out the bayonet lug. Her eyes went wide and she said, “Really?!? You HAVE to get one!!!” Have I mentioned I love my girlfriend?