For me, this Dissipator build started it all. I had set out to build my first AR-15 and I didn’t know what to build. The Dissipator had caught my eye and so the research started. It seemed only fitting to do my first build as my first build post. So lets jump right into it!
I covered Dissipators in my Intro To The Dissipator post. Lets rehash that a little bit though. So what is a Dissipator? For our purposes here it is a 16″ barreled AR-15 with a rifle length gas system and a FSP. It is a design that gives you the handguard space and sight radius of a 20″ AR-15, but also a softer recoil impulse. The down side is that it can be finicky and it might take some trial and error to get the reliability where you want it. They can, however, be pretty damn reliable once you get them all dialed in.
It started with an idea.
This whole journey began with an idea. I like a challenge when it comes to building projects. The idea of learning gas systems and how the AR operated via building a Dissipator seemed like a worthy challenge. I set out and researched parts and gas systems. It seemed as though many people had issues with low powered and steel cased ammo when building these rifles. That was unacceptable to me.
In my hunt for parts I found that barrels were actually a challenge to find. As much as people like the looks and idea of Dissipators, they tend to steer clear of real Dissipators. This lead me to JSE Surplus. They had Dissipator uppers built with a DPMS Dissy barrel at a reasonable price. Score. Essentially I got a milspec upper, semi-auto bcg, milspec charging handle, an A2 bird cage, a DPMS Dissy Barrel, and a non-free floated quad rail.
The lower receiver was something that I had not delved into before at this point. I had no idea what to do, what trigger to use, or what parts would best serve me. After acquiring a Hiperfire 24C to use, I ended up doing a little horse trading where that went out the window. In the end I traded the trigger for a complete PSA lower. A lot of people may turn away at hearing that, but at the time PSA didn’t mean anything to me and these days I’m more inclined to use Aero Precision, BCM, or something along those lines for a more budget friendly build.
The first iteration…
Parts immediately began to get ripped off and tossed into the parts bin. This all started with the lower. The trigger stayed milspec, but it did get a set of JP Enhanced Reliability springs, a Joe Bob’s trigger adjusting grip screw, and a set of KNS anti-walk pins. From there it also got a Battle Arms ambi safety, pins, a Magpul Miad grip, Magpul trigger guard, a Magpul CTR stock, and a Bad Lever. JSE recommended a carbine weight buffer (3.0oz), so that is what I put into it. It all seemed great except one problem.
This was when I learned about tolerance stacking and carefully choosing your parts. The trigger had an issue. While it had a nice crisp break, no take up, or slop to speak of, it was heavy. I tried a few different things to remedy the problem. Nothing seemed to work though and soon I realized that when the trigger got dirty, it failed. It didn’t take me long to get sick of this. The remedy was to just get a new trigger. I ended up with a Hiperfire 24 3G. And so a trigger snob was born… The cause of the problem did turn out to be the KNS Anti-Walk pins though.
The upper got some attention as well. I kept the handguard. The A2 bird cage was soon swapped for a Surefire Socom Brake. This make for a very flat shooting gun, but it is also incredibly concussive to people around me. The charging handle got tossed for a BCM medium latch charging handle. At this point in my life I was on the Magpul Fan Boy bandwagon and decided to jump on one of their Pro series rear sights. I’m still glad I did. I topped the upper off with an EO-Tech flat bottom 552.
After the trigger issue was remedied and the Dissipator was functional, then it was time to run the ever loving crap out of it. I found that with a carbine buffer and the semi-auto carrier it ran flawlessly. Even on cheap low powered and steel cased ammo. This was something the internet told me was impossible. It even held up in cold sub freezing conditions.
I ended up swapping a cheap Primary Arms 3x magnifier and flip to side mount on it. While the magnifier itself had no real issues and its quality was “okay”, I quickly destroyed the mount. I was not babying my gun and I wanted to see if I could cause issues and/or break it. The magnifier quickly got pulled off and forgotten about, although I still love an EO-Tech with a magnifier. I think this configuration shines on shorter guns that aren’t really reaching out past 300-400 yards.
In my testing I abused my Dissy. At one point running crappy dirty steel cased ammo with no cleaning or lube for right around 1000 rounds before I started to encounter serious issues. Keep in mind that this was an intentional user induced deal. I was purposefully pushing my gun to see what it would take to make it fail. I started having a failures to extract and big time. It turned out that my extractor was shot… completely toast.
The steel cased ammo debate rages on and perhaps that is what wore out the extractor. I cant say for sure though. Either way, I replaced it with a BCM extractor, spring, and o-ring. Then the gun was cleaned and lubed. It continued to run like a top and I have not had any issues with it since. I don’t expect any issues either. This is a gun that I would trust my life with in its current configuration and it has gone strong for thousands of rounds no without issue.
At some point you just get bored with your guns and you start modifying them further. I was at this point a couple of years ago. While small parts had come and gone, not much big stuff had changed. It was, however, time for a change in a major way.
The plan was to finally free float the Dissipator. I wanted to keep the FSP, so it would have to be a handguard that let me do so. In the end I settled on a Midwest Industries G3 Mlok handguard. It was much lighter weight, had Mlok on 7 sides, let me keep the FSP, and did not require timing the barrel nut. Let me emphasize how much I freaking hate barrel nuts that need timing. There are much better designs out there these days than designs that require timing. For example, I think BCM has it nailed and I would have used one of their handguards if they had one that would have let me keep my FSP.
If you’ve never removed a FSP before, then let me give you a run down on how I do it. First, get tooled up. I use a FSP block, the heaviest hammer I can get my hands on, and a big punch that I have ground down to actually fit the ends of the taper pins. Simply position the FSP so that the side with the small end of the taper pins is up and put it in the FSP block. This will keep the gun in place and allow the pins to drop out as you knock them out. Then you simple use your hammer and punch to knock them out. This can be hard as hell. I’ve had many FSP guns that had pins that refused to come out. Some with sub par pins that mushroomed. Then again, I’ve had some come out really easy.
How it sits today.
After the free float handguard only minor things have changed. It got a BCM short vertical grip, a flashlight, tape switch, an LMT Gen1 SOPMOD stock, ect. It even wore an old EO-Tech G23 magnifier that was slated to go onto my Block II SOPMOD build for awhile. After taking a class my light subsequently came loose due to me forgetting to loctite it. I was also swapping EO-Tech’s with a friend, so I’d be rezeroing no matter what. So I figured that it would be a perfect time to strip the gun, paint it, loctite stuff, and swap parts.
- Barrel: DPMS Dissipator Barrel
- Reciever: DPMS Upper
- BCG: DPMS Semi-Auto BCG with BCM extractor, spring, and o-ring
- Handguard: Midwest Industries G3 Mlok
- Flash Hider: Surefire SOCOM Brake
- Flashlight: Stream Light Protac-HLX in FDE on an Arisaka Mlok mount
- TapeSwitch: Streamlight tape switch with Cloud Defensive LCS mount in FDE
- Sights: FSP and Magpul Pro Buis Rear
- Optic: EO-Tech 512
- Vert Grip: BCM Mod 3 Mlok
- Lower Receiver: PSA
- Trigger: Hiperfire 24 3G
- Safety: Battle Arms Development Ambi
- Buffer: Carbine spring and buffer (3.0oz)
- Bolt Release: Magpul Bad Lever
- Grip: Magpul MOE-K2
- Stock: LMT Gen 1 SOPMOD stock with Arisaka QD adapter
- Sling: Vtac sling in Multicam with a Bubba Tab as a keeper.
Great post! I would love to see an accuracy test, as I’ve heard dissipators were extraordinarily accurate. How’s the accuracy on your build?
I’ve just it just barely sub minute with hand loads. I’m not the best shooter and on my 700 on decent days I shoot about 1 minute. When its bagged I can get it to shoot 1 to 1.5 minutes when I’m really trying with good quality ammo and the typical practice ammo I hose out of it is probably 2ish minutes. All acceptable for what it gets used for. Perhaps an accuracy test article and comparison might be a good idea. I have another dissy in the works as well as a handful of other guns to compare to.
What size gas port is on your barrel currently?
Will the gun lock back after the last round is fired if the gun is fired with a weak one hand grip, nothing contacting the stock?
Where does the brass eject to when fired normally with say, Wolf Gold 55gr .223?
Honestly I haven’t tried to hold it one handed and shoot it to see if it fails to lock back. I don’t think it would have a problem though. The dissy is certainly much more heavily gassed than something like my race gun or my 6.5 grendel, which is noticeably slow, but also has no problems with ejection thus far. I had to go back and watch an old video to check the ejection pattern on the dissy and with 193 it was 3-4ish o’clock. I would expect it to be a tad bit weaker with some wolf, but I have not had any issues shooting it even in cold weather.
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