I have been amassing parts for my latest AR project, a mock dissipator build, over the past few months. My upper/BCG should be here later this week from PSA, so I went ahead and put my lower together today.
I guess first I should explain the what and why of a mock dissipator. A few decades ago, when the carbine options for the M-16/AR-15 family were much more limited, people tried to find ways to shorten their full sized rifles down. One attempt at doing so was to make a dissipator, which involved taking a full length rifle, and chopping off the barrel right in front of the front sight post. This shortened the rifle by about 4 inches, but caused havoc as far as reliability and functioning. Enough gas wouldn't make it back to the BCG, because the bullet was leaving the barrel right after it passed under the ports for the gas tube. So dissipator rifles often would not function.
Fast forward to today, and several companies, including Palmetto State Armory, are offering "mock dissipator" uppers. These uppers generally have a mid length gas system with a low-profile gas block, as well as a front sight assembly out at the end of the barrel, the same distance from the receiver as it would be if there was a rifle length gas system. So these uppers are actually a 16.5" mid length upper, with a front sight post that serves as just a sight/attachment point for handguards, not as a part of the gas system.
At this point, someone is probably going, well, why not just buy a normal mid-length carbine? There are two things I generally don't like about a lot of AR carbines as it relates to my shooting style. First, they have a rather short sight radius. Generally speaking, the longer the sight radius, the better. A Mock dissipator solves that issue by having the front sight at almost the end of the barrel, effectively giving an extra few inches over a normal mid-length or carbine length system rifle. I like optics, I think that they are one of the biggest leaps in individual kit for infantryman in the past 50 years. But, I am also a firm believer in knowing how to shoot with irons, and having back-up irons on my rifle. Because of this, I want a rifle with the longest sight radius possible, while still maintaining the short length of a carbine. Second, I like to run my VFG and light pretty far out on a rail. Having a light far out there eliminates any light shadow from the barrel, and the VFG being further out helps with control during rapid fire. The ability to use rifle length handguards and rails means that I can place these as far out on the rifle as possible, right up by the muzzle.
And for those who are asking "why not just get a full sized AR-15?" Because I wand to maintain the lighter weight and maneuverability of a carbine. It is hard to work indoors with a rifle with a 20" barrel, not impossible, but not as easy as it could be. Same thing for getting into and out of vehicles.
So, now to the nitty gritty of the lower, I will talk more about the upper and it's specs when it gets here later this week.
The lower itself is an Aero Precision lower. It is marked for multiple calibers, and has pictograms instead of the words "safe" and "fire." Other than that it is the same as most other metal AR lowers, nothing special.
I went with one of PSA's MOE lower build kits. I couldn't find any flaws with any of the parts, and they were all included as advertised. It came with a mil-spec buffer tube and Magpul MOE stock, trigger guard, and MOE grip. As well as Palmetto State Armory's standard weight buffer.
Other add ons that I decided to add: A Noveske short throw ambi safety lever. I don't have any experience with Ambi-safeties on AR's but I wanted to give one a try. If I need to change it to the more traditional style, that wouldn't be hard to do.
Magpul ASAP sling plate: Even though I am starting to like my Vickers VTAC more and more, I still like having a sling plate on my rifles for single points.
Putting it all together took me just a little over an hour, taking my time and paying attention to what I was doing, while referencing ITS tactical's build guide. I didn't run into any significant issues, building an AR lower really isn't difficult as long as you take your time.
Here is the finished lower:
And the ambi lever on the other side: