Previous posts in the series:
So, after getting a great deal on the upper and lower, I needed to start getting the rest of the parts. This is where it got complicated.
It seems there is no “mil-spec” for the AR-10 style rifle because they were never made for the military. Apparently there are two primary styles with different variants and even more “one-off” types from various manufacturers.
The two primary styles are the Armalite style (this is the only style, by the way, that can really be called the “AR-10” since AR stands for “Armalite Rifle”).
Armalite style AR-10’s come in two variants: A series and B series. They are not interchangeable as the receivers are milled differently. The most obvious difference between the two are the magazines. The A series uses magazines that look much like a scaled up AR-15 magazine. This magazine style became the “standard”; it’s used in DPMS lowers and is produced by many aftermarket manufacturers including Magpul. The B series uses an aluminum magazine based on the M-14. The magazine release and bolt catch are also different.
The other primary style is the DPMS pattern. There are a few different variations and many manufacturers that produce receivers ostensibly in the DPMS pattern do so in non-standard ways. Basically, there is no guarantee that uppers and lowers from different manufacturers will work together even if they describe themselves as DPMS pattern or Armalite pattern, and DPMS and Armalite definitely won’t work with each other. It seems to be the best bet to buy the upper and lower from the same manufacturer to ensure they’ll work correctly with each other.
In addition to the uppers and lowers being different, many of the other parts are specific. One of the big differences between Armalite and DPMS style rifles is the barrel nut threads. Armalite uppers take a 1 7/16″ barrel nut threaded at 18 teeth per inch (TPI). “Traditional” DPMS uppers take a 1 7/16″ barrel nut but threaded at 17 TPI. More recently, DPMS has introduced a generation 2 upper that takes a 1 5/16″ barrel nut threaded at 18 TPI.
There are also three variations of DPMS upper height. The two main ones are high and low. The third one is apparently rare and is called “high rise” or “slick side”. This becomes important with railed handguards. If you get the wrong handguard for the upper height, the rails won’t line up.
Whew! Talk about confusing.
One thing that helps is that some of the parts are interchangeable with AR-15 components. I found this handy website that goes through all the parts and what is interchangeable.
Just in case that isn’t confusing enough, it turns out that my Diamondback receivers are sort of a combination of DPMS and Armalite.
The rear of the upper and lower where they fit together (the area between the takedown pin and the buttstock threads) are shaped like an Armalite (DPMS is more rounded there), but the upper takes a “traditional” DPMS barrel nut and matches the DPMS high rail profile.
The lower apparently works best with Armalite series A parts (I figured this out through trial and error). I read in the reviews that only Diamondback proprietary pivot and takedown pins will work, so I ordered them, but then I read later that Armalite A series pins work…I didn’t try those, but based on other discoveries I made, I’d guess it’s probably accurate.
At any rate, here’s what I ended up using:
Upper and Lower: Diamondback
Barrel, extension and barrel nut: DPMS (traditional) style
Gas block and gas tube: AR-15
Bolt and bolt carrier: DPMS style
Charging handle: AR-15
Handguard: DPMS high
Ejection port cover: DPMS
Forward assist: AR-15
Takedown and pivot pins: Diamondback*
Takedown and pivot pin springs and detents: AR-15
Safety, safety spring and detent: AR-15
Fire control group: AR-15
Buffer and buffer spring: DPMS (these are interchangeable with Armalite)
Buffer retainer and retainer spring: AR-15
Magazine release: DPMS (modified**)
Bolt catch, spring, detent and roll pin: Armalite series A
*As I previously mentioned, I bought proprietary takedown and pivot pins from Diamondback, but I read elsewhere that Armalite A series pins would work. My guess is that’s accurate based on the fact that I needed an Armalite A series bolt catch.
**The DPMS magazine release “almost” worked. I’ll go into more detail later, but I had to “make” it fit.
More to come…