My Dissipator build

[GunnyUSMC]

I remember back in the 80s when I saw my first Dissipator, man did it look so cool. I wanted one bad. About 3 or 4 months later I was able to hold one in my hands and I was disharted. It had a heave barrel under the handguard that was right at an inch thick. This made for a very heavy carbine.
Years later I read about Dissipators with light barrels, but these had barrels with carbine lenght gas systems with the sight tower mounted at rifle lenght. I didn't care much for the setup and pretty much gave up on the idea of getting one.
Last month a friend went off the deep end and spent $2000 for one of the Tiger McKee Katana carbines.
http://shootrite.org/katana/katana.html
After having a look at it my love for a Dissipator came back.
I checked with my Gunsmith friend to see what options I had for building one with a light barrel. He told me I could get a Dissipator barrel and he could trim it to a lighter conture for $50, or I could get a 20" barrel with the light conture and he could cut and rethread it to 16" for $75.
Well I had a 20" FN barrel in my shop and a few days later I was at my friends shop having it cut down. We did some horse treading for the work and my out of pocket cost was about $10.

Here is the barrel after having it cut,






Then mocked up to see how it would look.


I started getting the parts.


I went with an old styl three prong flash hidder and coated the barrel with Aluma-Hyd II Matt Black.
I wanted it to have a little different look so, I coated a few other parts with Aluma-Hyd II FDE.
I took it to work and fuction tested it and it wirked great. I hope I can make it to the range with it next week.

 

[Gtscotty]

I'm not really one for Dissipators, but i like that. Out of curriosity, did you have to open the gas port up some to make up for the shorter time the port will be exposed to high pressure gas?

 

[Sapper771]

I am wondering about that as well. Most Dissipators I have seen have 16" barrels and carbine length or mid-length gas systems. I would be concerned about not getting enough gas to cycle the action.

Good looking rifle. I have always wanted a Dissipator too, just havent committed yet.

 

[GunnyUSMC]

Depending on who you talk to or where you look up your info, you will get a different story on what gas systen and barrel the first Dissipators had.
The first Dissipator I picked up in the mid '80s was made by Bushmaster. I think at that time Bushmaster was the only ones making them. The rifle had a 16" barrel with a rifle lenght gas system. The barrel was heavy as hell. Later on when I put my hands on one with a shorter gas system, the barrel was still on the heave side, I didn't care for it after shooting it. The handguard would get hot where the gas block was.
When building one with a rifle lenght gas system, you have two issues to worry about. One, like with any AR, is ammo. There is stuff out there that is not loaded to Mil Spec and can cause problems.The maine issue is the gas port. Most often the gas port needs to be opened a little more depending on the barrel you use. The barrel on my build is a FN Govt. profile made to GI spec.
When I had the barrel cut my friend checked the gas port and side that it was large enough and would work, he was right.

 

[bannockburn]

GunnyUSMC

Like the look of your Dissispator build, especially the two tone color combination of matte black and flat dark earth.

 

[1KPerDay]

Nice work. I have always loved Dissys. Here's my "mock dissipator" build from PSA (mid-length gas). Cav arms A1 stock.

 

[tahunua001]

very nice. I just got done with a 16 inch PSA build myself, although mine is just a carbine handguard and gas system, and chambered in the pride of the commies cartridge. with cheap ammo I'm pulling 2 inch groups but hope to shrink that down with some handloads. I'm currently in the process of selling my dissy, not getting the accuracy or enjoyment out of it that I'd like so I think I'm going to go higher end with a Seekins if I ever offload the old one.

 

[Theohazard]

That's an awesome build, Gunny. I like it a lot. But I have a question: I always thought that in order to be a dissipator it had to have a low-profile gas block with an A2 sight close to the end of the barrel that acted as a sight only and not a gas block. Like this:

I thought it had to have a setup like this in order to qualify as a dissipator. And the purpose was to give you maximum sight radius while still having a traditional gas system length. Am I wrong on this?

By the way, I'm definitely not trying to criticize your build; I think it's awesome and I'll bet with that short dwell time it shoots really smoothly. I just want to make sure I completely understand what a dissipator is.

 

[MachIVshooter]

Looks good!

Years later I read about Dissipators with light barrels, but these had barrels with carbine lenght gas systems with the sight tower mounted at rifle lenght. I didn't care much for the setup

Why? I mean, I get that it's not a "real" dissipator, but aesthetically they are the same, and with a proper dwell time (at least the 16" mid length dissys are). Other than the tiny gap that results from pinning a .750" FSB to a .720" section of the barrel, you'd never know without taking handguards off. I chose an MOE middy dissipator upper for my build on an Ares billet lower with Luth AR skeleton stock:

 

[wally]

Theohazard, I'd wager that these days the photo you show is the way most of them are made.

I'm liking a low profile gas block on a carbine with a 15" free-float handguard more than the dissipator these days.

Although the dissy prolonged my ability to use iron sights for a couple of years as my presbyopia slowly worsened. For me now, irons are only for emergency from a failed optic (I use QD mounts) but its really little better than "I fart in your general direction" effectiveness if I actually have to use irons

 

[Destructo6]

According to Jim Sullivan, the AR needs about 7" of barrel in front of the gas port for proper dwell time, port pressures, etc.

So, I'm guessing with the Dissipator style, you get that 7" in front of the gas port, the longest sight radius possible (ie that of a rifle), and a short-ish barrel?

Interesting concept.

 

[1KPerDay]

That's an awesome build, Gunny. I like it a lot. But I have a question: I always thought that in order to be a dissipator it had to have a low-profile gas block with an A2 sight close to the end of the barrel that acted as a sight only and not a gas block.

Modern "mock dissipators" have mid or carbine gas with full rifle sight radius. True original dissipators have rifle gas.

 

[Nature Boy]

I've always liked the Dissy.

I may eventually make an upper. It's on my "list"

(So many rifles, so little funds )

 

[horsemen61]

Can someone explain to me the dissipator concept and why it came about?

 

[GunnyUSMC]

The reason I don't care for the shorter gas systems on a Dissipator is that when working the rifle hard the area where the gas block is gets hot. Most often that is where my forward hand is.
If I remember right the Dissipator concept was aimed at the military, to have a short barrel rifle with a longer sight radius. It used a heavy machine gun barrel to help with control with full auto fring. Back in the 80s there weren't a bunch of compact electronic sights like today and the longer sight radius was an advantage on a carbine.