The modern Dissipator has very interesting roots. Despite its ancestors dicey beginnings, modern Dissipators can make for great rifles. So what is a dissipator? Well, we’re about to get to that.
I suppose you could say the Dissipator derives itself from the M16A1. All small frame AR pattern rifles do. It has a more colorful history than that though. Its roots go deeper than just sharing a platform. It all started when Colt decided to make a carbine length rifle in the AR pattern. The result was the Colt 605.
The Colt 605 was not a resounding success. It only saw limited use and that use was, from my understanding, mostly special operations. It suffered from one major issue. Reliability. It was not known to be a reliable rifle. This is due to the same reason why most people would consider the modern Dissipator unreliable as well. Dwell time…
Deeper into the 605.
So what made the 605 unique? Well, as I mentioned it was Colt’s first carbine length rifle in the AR pattern. It came in two variants, the 605A and the 605B. The difference bewteen the two was in the fire control group. The 605A’s fire control group had safe, semi, and auto where as the 605B had safe, semi, auto, and burst.
Where this rifle varied from its 20″ brethren was its shorter 15″ barrel. Yes, you did read that right. Its barrel was 15″ long. In most modern day AR-15’s you would see a carbine length gas system or perhaps a mid length gas system on a barrel of that length. The 605, however, retained its rifle length gas system. This greatly reduced the dwell time from its 20″ relatives.
The 605 retained much from its cousins. There were multiple variations of upper receivers, however, none that I am aware of had a forward assist. The uppers were, obviously, older carry handle style uppers. The bolt carrier itself also reflects the lack of a forward assist and was chrome plated. Partial fenced lowers were used. As noted before they had a 15″ barrel that was rifled gassed with a 1:12 twist. It is my understanding that they also used the edgewater buffers.
This made for an interesting rifle that was shorter than the M16A1, but the reliability was lacking. This was due to the gas system. Being rifle length on a 15″ barrel means that there is very little dwell time. Dwell time is the measure of time that it takes a bullet to move from the gas port to the end of the muzzle. This is an important because that is the time that gasses from the spent round can cycle the rifle. Essentially the 605 has substantially less time to pressurize the gas system and cycle the rifle.
Lets fast forward a bit.
I am unsure of when exactly modern Dissipators came on the scene. There are some discrepancies and controversy here. What I do know is that the term Dissipator was not used for the 605 and was actually coined MUCH later by Bushmaster. It is my understanding that Bushmaster also did not stay true to the design of the 605.
Bushmaster’s Dissipator had a major difference in how it was setup. Where the 605 and what I consider to be a Dissipator have a rifle length gas system, the Bushmaster variant had a carbine length gas system with a low profile gas block hidden under the handguard. It still had a pinned FSB in the rifle gas position, but it only functioned as a front sight. It also had a 16″ barrel. One could assume the reasoning behind this was to keep it out of NFA territory without pinning a flash hider.
Today many manufacturers make “Dissipators” like this. That being with carbine or mid gas systems hidden under the handguard. You may also hear people call these “mock Dissipators.” That is how I refer to them as well.
Are you Mocking me?
Most AR pattern rifles with a barrel shorter than 18″ to 20″ use a gas system shorter than rifle length. This adds dwell time and aids in reliability. This is the philosophy behind running a shorter gas system and a low profile gas block under the handguard of a mock Dissipator. Many people would deem the mock Dissipators to have superior reliability over an actual Dissipator.
When people often ask what the allure of the Dissipator is, I usually see a few different answers and a lot of opinions backed by no real experience behind the rifles. Keep in mind, I consider people who have only run mock Dissipators as not having having experience. People will say things like the sight radius from a 20″ AR allows you to be more accurate than with a shorter sight radius. Its usually also mentioned that there is more handguard space.
This is all true. There is also always that one guy that will remind you that an AR with a low pro gas block in the carbine position with a 15″ hand guard and a front sight at the end of it trumps the Dissy in every way. Hence in their eyes the Dissipator is irrelevant in every way except for looks. This is where a lot of people agree and move on. What if I told you that they’re wrong?
Don’t knock it until you’ve tried it…
People with no experience behind a real Dissipator often don’t realize that there is an advantage to the rifle length gas system. Mind you, all Dissipators these days have 16″ barrels and slightly more dwell time then their 605 relatives. We also have manufacturers upsizing gas ports for more reliability as well.
When people say that the only upside to the Dissipator is sight radius and handguard length, they often are leaving out the coolest thing and in my opinion a major advantage. They shoot like a god damn BB gun. Dissipators have the most mild recoil impulse out side of building a highly tuned race gun. Granted, this is also dependent on gas port size, but they still shoot incredibly soft.
So is reliability worth a soft shooting gun that has a long-ish sight radius? Lets talk about that?… Yes… but wait until you hear me out.
The meat and potatoes.
I’m going to tell you a secret. You can build a reliable Dissipator. Some times it takes work to get them to run reliably and there are a myriad of factors that will determine its reliability. Different manufacturers use different gas port sizes on their barrels. There is also buffer weight. The weight of the carrier can also play a role. Essentially what I’m saying is that all the reciprocating mass in the upper and the gas system have to play nice with one another.
Some times it takes some trial and error in your parts selection to get them to run right. More gas means more recoil impulse. DPMS, Del-Ton, and Spinta Precision all make rifled gassed Dissipator barrels and they are all gassed differently. There are a lot of gas port size numbers tossed around on the internet and honestly its hard to remember who uses what size off the top of my head. I run DPMS and Spinta on my guns though.
You also have to worry about your buffer and carrier weight. I’d say your best bet is to go with a carbine weight buffer (3.0oz). I’ve heard of people modifying their buffers to make them slightly lighter, but I’ve never needed to or attempted to do this. An H1 and heavier buffer will likely not result in a gun that runs reliable. It also might not run with a much heavier buffer. Also your carrier weight can be a factor. On a Dissipator I like to stick to semi-auto carriers because they have material removed and are lighter. That is not to say that a full auto carrier wont work though. I’ve found that a winning combination is a DPMS HBAR Dissy barrel with a semi-auto carrier and a carbine buffer. The idea is to minimize your reciprocating mass without running out of spec parts or race gun parts.
I do have my reasons for doing all this and for loving this setup so much. First of all, once you find a combination of parts where everything is in tune, then you end up with good reliability. You don’t have to run a light weight bolt carrier or any parts that will compromise reliability. That FSB up front also has one more major advantage to it.
What am I talking about? Well, you have a pinned front sight base. Why is this good? You get a long sight radius. That’s not the only thing you get though. You get a bomb proof gas system. That FSB is not moving. It will not rotate or slip on you causing your rifle to lose gas. You’re not going to break it. There are very few low pro gas blocks out there that I trust more than a pinned FSB.
As far as reliability goes, you might ask how many failures I’ve had and I’d reply, “very few and the ones I did have were operator error or intentional.” Intentional? Yes, I’ve personally pushed my gun to see what I had to do to make it fail. You will often see people say that they’re AR’s run flawlessly so long as they aren’t dry. I’ve found this to be the case as well and I’ve also found that my main Dissipator is no different. I’ve only had failures from a worn out extractor and from being bone dry. We’re talking over 1K rounds with no cleaning… and bone dry.
With all this said, I’m a firm believer that if built right, then a Dissipator can be a good dependable rifle. There is still a stigma floating around the forums though.
Wrapping it up…
I’ve rambled on awhile, but I think you get the point. If you build a Dissipator right, then you get a rifle that is reliable and handy. Perhaps the downside is that there might be some trial and error to make it reliable and that the source for light weight barrels are few and far between. I’ll talk about that in a different post. Perhaps I’ll even spend some time tracking down all the manufacturers that still make Dissy barrels and post their barrel specs. This could be quite helpful for those who want to build one.
I’d honestly say that if you’re interested in a Dissipator, then go for it! Build to your hearts content, just remember that you may end up having to play with it to get it reliable. It might not be for the faint of heart either if this requires opening up your gas port a tad bit. I’d also like to say that if you only are going to have one AR-15, then don’t make it a Dissipator. Get something that runs out of the box and that you know is 100% good to go.
Once you do build a well running Dissipator it becomes really hard not to fall in love with it. In the near future I will be doing more Dissipator content. If you’re interested, then stay tuned because I have one Dissy build coming up. I’ve also been strongly considering building the the holy grail of Dissipator fanatics… a 605 clone. I will also be eventually spot lighting my Dissipator and Racipator (Race Dissipator). Hell, I can neither confirm nor deny that mini Dissipators are a thing. You’ll just have to stay tuned to find out.