This is a repost of my thread from another forum, but I think it's pertinent here as well.
I'm a big fan of the LaRue Tactical rails. They are about as close to perfect as you can get.
But, when I saw the Crane-built Daniel Defense Mk18 RIS II equipped 10.5in guns, I had to build myself an upper.
Now, I figured rather than building a hobby gun, I might as well make this a top-quality fighting gun that I can use for work and that would make it through a 3-day carbine course without issues.
I started this project when parts were tough to come by, and in some cases I had to wait months to get what I wanted. But, waiting proved to be worthwhile, as I was able to acquire the components I originally spec'd for this project. They are as follows.
Upper:
-Anchor Harvey forged flat top upper. I don't know the exact manufacturer.
-Sabre Defense 10.5 inch 1/7 chrome lined barrel with extended (M4) feed ramps
-LaRue Tactical .750 low profile gas block
-Colt carbine-length gas tube
-KAC Flash Hider / QDSS supressor mount
-Daniel Defense MK18 RIS II free float rail
-Lewis Aerospace M16 Bolt Carrier Group with Crane O-ring, black insert, and extra power exractor spring
-Standard charging handle
Lower:
-Firebird Precision lower
-CMT lower parts kit
-BCM 6-position receiver extension
-LMT SOPMOD stock
-Magpul MIAD grip
-Magpul aluminum enhanced trigger guard
-H3 buffer
-Chrome Silicon buffer spring
-Daniel Defense ambidextrous Burnsed Loop sling mount
Optics / MISC
-EOtech SU-231 PEQ (553)
-Troy Industries front/rear BUIS, Tan
-prototype gangster grip
-ACE rail-mounted fixed sling loop
-Blue Force Gear VCAS
Building the gun went smoothly, and the DD rail was very easy to install. Everything went together as planned, and I was off to the Scottsdale Gun Club for a live fire function check. Everything worked like a charm.
I've since then put about 2,900 rounds through the upper. While on a trip down to Yuma Proving Grounds, some Marines and I put about 1,600 of those through this upper on full auto while mounted to an M16A1 lower, as pictured here:
There have been other lowers that hosted this upper, but the majority of the rounds fired with this upper have been on the Firebird lower. A few words on this piece; I honestly hadn't heard of Firebird Precision until browsing around one day at the Scottsdale Gun Club. In need of a quality lower to start this SBR project, I checked them out. The machining, anodizing, and engraving are all top quality. Some extra features, once of which that I won't likely utilize, are the set screws for reciever tensioning and trigger pre-travel. I set the trigger screw to what seemed like most comparable to my LMT lower and applied red Loctite 262. I haven't noticed any shift after thousands of rounds fired. If you are looking for a stripped lower, I recommend giving them a look. It is a mil-spec lower and works like a charm with the CMT parts kit and other components.
The only issues I've had (some double feeds) were with the use of some HK "high reliability" ( Bullshit ) mags in Yuma. When using P-mags, the function has been perfect. I keep the gun lubed with Mil-Comm MC3000 semifluid. During the inital 100-200 rounds, I kept the gun lubed with extraneous amounts of Break Free CLP, and cleaned it after 100, then 200 rounds. After this, I've used the MC3000. I lube the gun quite generously, but don't re-apply often as the lube doesn't burn off except on the tail of the bolt.
The gun balances very well, and handles great on full auto. There is little difference in handling compared to a 14.5 inch M4, but it seems to me the ROF is a bit higher due to the larger gas port in the 10.5 inch barrel.
Ammo used thus far:
PMC Bronze 55gr FMJ
Wolf 55gr FMJ
PRVI 55gr FMJ
BH 55gr FMJ
LC 62gr M855 green tip
Hirtenberger 62gr M855 green tip
Wolf 62gr FMJ
PRVI 75gr OTM
BH 77gr Moly-coated OTM
Mk262 MOD 0 & MOD 1