After reviewing options, I settled on finding a suitable complete upper, buying a stripped lower (the actual firearm from the ATF's perspective), and ordering the remaining small parts needed to complete the rifle. This also gave me an excuse to build an upper as a future project. Looking around at features and reviews led me to LaRue's Stealth Sniper System. These uppers are available with 12", 16", 18", and 20" barrels and rail systems ranging from 7" to 13.2". I didn’t seriously consider the 12" barrel due to velocity loss. Further research indicated that dropping from a 20" to a 16" barrel would loose about 150 fps, which changes the point of impact less than 2” at 300 yards. See also thread 1, thread 2, thread 3, thread 4, and this experiment for discussions on 16” vs. 18”. I debated between the 18” and 16” and eventually went with the latter to give a slightly more compact rifle. That led to the next question: rail length. I knew that I wanted to mount a shooting sling to the front of the rail, so I got into several shooting positions with my M4-style AR-15, saw where my hand gripped the handguard, and added a few inches for mounting the sling and giving additional room for a bipod. This gave me an 11" rail, so an order for a Stealth upper with a 16" barrel and an 11" rail went in to the good folks at LaRue. You can order one of their billet lowers along with each upper, so I signed up for one of them as well and arranged the transfer through a local firearms dealer. These days, LaRue sells their lowers without the purchase of an upper.
The next step decide on and order the remaining parts. I knew that I'd be using a scope with a 30 mm tube, which made a LaRue SPR mount a natural choice. A Geissele DMR trigger was similarly easy given my experience with the one in my other AR-15, which is built from mostly Rock River Arms parts. I originally learned about the Geissele through this comparison of triggers. A pair of GG&G Sling Thing detachable sling mount, one each at the front and back of the rail, would let me attach BlackHawk sling in a CW sling configuration. MagPul XTM rail covers looked like a slick way to protect the rail and keep it from grating my hand when shooting. Other items for the lower included a DPMS parts kit, Hogue OverMolded pistol grip, and Vltor Mil-Spec Modstock buttstock assembly. The latter looked like it would provide a fine cheek weld.
The upper arrived before the lower, so I attached it on my Rock River lower, mounted the IOR 6x42 (discontinued) scope from my A-Bolt using the LaRue mount, and headed to the range. This lower uses a basic commercial 5-position stock and Geissele DMR trigger. The combination shot wonderfully, and I had little trouble scoring 5 for 5 on 8" plates at 300 yards using cheap Wolf 62 gr. ammunition shooting prone unsupported with the sling.
The lower then arrived, and the rifle was complete in less than an hour. All that's needed to assemble a lower is a drift punch set, a stock wrench, and screwdrivers. The main challenge is preventing the springs from flying across the room. The DMR trigger dropped right in with only a minor overtravel adjustment. But something happened during the next range trip: I kept seeing black around the edge of scope's field of view as if my eye was too close to the scope. The Modstock provided a great cheek weld as expected, so what was wrong? I got out a tape measure when I arrived home and measured the stock's length. Turns out that Mil-Spec stocks are on average an inch shorter than the commercial assemblies like the one on my other AR-15. I did some research online and ordered a MagPul ACS buttstock, which would give me back that inch and provide the same cheek weld. It worked like a charm! Note that you need to order the sling swivel separately. Also, Vltor now makes an EMod stock that provides an extra inch in length.
The rifle looks beautiful and it shoots better than I expected. I put over a thousand trouble-free rounds through it across the first four range trips, and it’s continued to run smoothly since then. Cycling is wonderfully smooth, and everything about it exudes quality. I attribute much of the smoothness to the mid-length gas system. It’s not as smooth as a rifle-length system, but way better than carbine-length ones The light, crisp break on the DMR trigger makes it easy to release the shot without disturbing the crosshairs. Hits outside the 10-ring are misses when shooting on paper. A friend that had never fired a rifle before went 3 for 5 shooting a 2-pound hammer head at 300 yards off a rest with PMC 55 gr. ammunition (the support broke and dropped the head on the third hit). I haven't noticed a shift in the point of aim as the barrel heats up.
In mid December 2009, I swapped out the IOR 6x42 scope for the updated IOR 2.5–10x42 FFP scope that I ordered from Scott at Liberty Optics (great guy and very knowledgeable—he’ll be getting my business in the future).
The main changes from the previous version are exposed target knobs. I had considered the Super Sniper 10x42 HD, Nightforce 3.5–15x50 FFP with 0.1 mil knobs, and Premier Heritage 3–15x50 prior to ordering the IOR. The image on the 2.5–10x42 isn’t quite as crisp as the 6x42, but more than good enough. The mil turrets made it extremely easy to sight at 100 yards and recenter the group up at 300: no need to convert mils to MOA in my head. My only criticism of the scope is that zeroing the turrets requires a jeweler’s flathead screwdriver. IOR should have used standard-size hex screws.
The nylon CW sling didn’t work out so well in that it continually slipped my arm. I replaced it with a Turner biothane 1907 sling, which stays put.
The following picture shows the complete rifle prior to adding an AAC SPR/M4.
The rifle shoots 1.25–1.5 MOA running Hornady TAP Training 75 gr. with a Harris bipod with a QD mount. I can get consistent hits on clay pigeons at 350 yards but not at 400.
Overall, I’m quite happy with the rifle. If I did it again, I’d roll my own upper using a rifle-length Vltor VIS and an 18” barrel with a rifle-length gas system. The extra 2” of barrel wouldn’t appreciably affect handling, and the longer gas system would provide an even milder recoil impulse. I’ll enjoy shooting out the 16” barrel in the mean time. The 11” handguard is also about an inch too short for optimal mounting of both a sling swivel and bipod.
Last edit: 27 September 2011