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Anyone build a dissipator style upper?


Well-known member
May 23, 2020
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I have a couple lowers on the way. One has an upper ready, one doesn’t. Thinking about some form of dissipator style build. I read about some gassing issues, that could possibly be remedied by drilling the hole in the barrel slightly bigger.

Most dissipators today are nothing but a carbine or mid-length gas system with a longer handguard and front sight post. This means they will function identically to one with a shorter handguard.

They arent all the common since you can you can just go to a free float rail and have all the space and sight radius you want. I still like the idea for an iron sight only gun though where you want the durability of a FSB.
Yes, I did more reading yesterday and I should have asked about a “605” instead of a dissipator. I am curious what is involved in making a 16 inch barrel with the rifle gas system function correctly. I have some sort of a retromod type upper in my head.
Yeah I like the concept. I’ve thought about putting together something like this. Im just not sure why you’d mess with drilling gas ports out and decreased reliability when you could just run a 14.5” or 16” barrel with a midlength low profile gas block and then a rifle FSB and hangduard.

Becuase I don’t have one yet haha. I do understand that that is what a “dissipator” was, and I was a dumb dumb for calling it that.
At the moment, I don’t think I can just click and buy a true dissipator barrel. Everything I found is discontinued.

edit: I did it again! I mean a 16 inch barrel with a rifle gas system.
After more reading, I think I can figure this out. Looks like people drill out the gas port to .110 and call it good. However, I believe they are using rifle buffer systems, I plan to use the new ke arm mk3 lowers, carbine buffer system. Because of the different buffer system, a heavy buffer may be needed, H2 seems common. So, brownells is making 605 clones. They have complete uppers available, but they are 15.5 with pinned and welded flash hiders. They also have just the barrel assembly, with no flash hider. Faxon sells flash hiders that are.620 OD, so you can slid the front sight on/off without removing it. So that barrel, that flash hider pinned/welded, drill hole to .110 if it isn’t already. What am I missing?

I see in my head a carry handle slick side upper, a full length free float hand guard, with a front sight blade, on the ke arms mk3 lower. Just irons, no anything else, except maybe a sling.

Someone build this so I have something to copy.



I don’t see it being reliable with a variety of ammo given the super short dwell time and especially with a carbine buffer. The rifle length (and A5) buffer setups are apparently more reliable/forgiving. You can probably get it to run with with a specific load however, with some tuning, as long as it’s cleaned/lubed. I also don’t really get the point of the polymer lowers other than if weight savings is the main priority. Especially in an AR where it is “the gun” and you can’t just grab another for $30 off eBay.

To me, both of those things go against the concept of a KISS, iron sight AR, which would be a no-fail apocalypse weapon. I’m interested to see how it goes however, so carry on and keep up posted.
All valid points.

No particular reason for the polymer lowers. I ordered 2. I already have an upper for one. They are pre order only at the moment, a claimed late 2nd quarter 2020 release date.

Dare to be different and all, you know. I change my mind about every 14 seconds.
PSA has dissipators with a midlength gas system and a pinned A2 front sightpost with full length handguard. Something about the barrel length, dwell and gas system that makes dissipators a little less reliable, but this fixes that issue(?)

I built one and it is my echo trigger platform. Gassed perfect out of the gate and never fails to go bang :D
New question!

So ideally, I want a slick side, carry handle upper, preferably with a brass deflector. However, that is not a thing (except a “model 750”, which I’m not going to find for a price I’m going to spend).

The brownells retro upper is all those things except no brass deflector and no M4 feedramps.

How much would I hate that over just getting a flat top slick side and adding a carry handle?

I read that a lefty can eat some brass in the cheek without the deflector. I am righty but sometimes lefty’s touch my things that go bang. The feedramps seem like a worthwhile upgrade.
I have to ask a question, why? I mean from a ergonomic point the style is way out of date, far better and lighter tech has come along. I guess I don't get the "old look just because" thing.
Because I want to put together something I haven’t seen anyone else do. I understand it’s kinda dumb, like hopping up a Subaru. I already have 10.5, 16 in both carbine and mid length gas, and a 15.5 mid length gas. But I don’t have a 16 inch rifle gassed upper. It seems everyone that does a 605 style, they try to copy the prototype. I envision a more modern, updated version.

How much will I hate the brownells upper over a, let’s say, aero precision slick side flat top?
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Brownells site does say the 605 complete upper is for a rifle buffer setup, so I kinda figure worst case I put one together.

Edit: it also says use 5.56 55gr ammo, and the gas port is .1015.
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I bought a PSA dissipator upper a few years ago and it runs great. I use an A2 rear sight because if you want accuracy with iron sights there’s no reason to run an A1 sight.
No help on the upper, but from the reading I’ve done the m4 feed ramps are really just a reliability mod for full auto. The only combination you don’t want is a cut upper with a non- cut barrel, as the tip of the bullet could potentially get hung up there.

I’d probably just go with one of these and a bolt on carry handle, as you aren’t trying to build a clone. That way you can always take it off and put an optic on if you want something different in the future.

Bronco, pics?

Gator, I’ll have to look again but I don’t think that barrel has the cuts. So you think I should just get the brownells upper? I haven’t bought anything yet, haven’t looked at anything for a few days, but that upper was on sale like a week ago.
Just a basic gun. It came with the magpul moe handguards and SS heavy barrel with mid length gas. I don’t know who made this barrel for PSA but it’s a good one. I put a set of trijicon night sights on it for nocturnal uses.
edit: added pic with A2 handguards.


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I set mine up as a simple build as well. I have a Fostech magnesium lower and it is super light. One of my favorite "property patrol" rifles.

D jeeper and bronco, are those both psa carry handles? Do the giant knobs make you....irate? One thing I don’t like about that style carry handle is how bulky the knobs are.
D jeeper and bronco, are those both psa carry handles? Do the giant knobs make you....irate? One thing I don’t like about that style carry handle is how bulky the knobs are.

I don’t recall if it’s colt or something else, it’s got a cerro forge mark on it. I know it lines up with F marked sights, and not all of them do so pay attention to that. The jumbo knurled nuts don’t bother me at all, but it would be an easy fix to change them out.
D jeeper and bronco, are those both psa carry handles? Do the giant knobs make you....irate? One thing I don’t like about that style carry handle is how bulky the knobs are.

I honestly do not even notice them. They might be bulky, but they do not stick beyond the receiver much.
Progress has been made!

Last January when the ke arms kp15 lowers were announced, I preordered 2 stripped. I got my hands on a low serial numbered black one on Christmas. I promptly started dremeling and drilling and tapping holes. I am very impressed with it. Nay say all you want, but until you have one in hand, I will disregard all criticism regarding the lowers. This is a superior product in my opinion.

Anyways, I have come up with a plan for the upper. I still do not know if it will cycle reliably with a carbine buffer. If not, I will build a rifle lower.

I ended up ordering the brownells 605 barrel and slim Faxon muzzle brake. I have the aero altas one 12 inch mlok hand guard that I intend to use, it comes up directly behind the rifle length sight post. I am still trying to find a black slick side carry handle upper.

Both ke arm lowers will be pretty much the same, I ordered both colors. I have most parts to finish the second one, but not everything yet.

I used ke arms slt2 trigger with their 45 degree ambi safety (can put on safe when hammer is up), aero pdq lever (ambi bolt release), Norgon ambi mag release, jp enterprise buffer, and grov tec threaded sling mounts.

I had to dremel on it some for the pdq lever, I drilled the hole for the safety detent all the way through and tapped it from the bottom to hold the spring, and tapped the holes for the sling mounts. I only used 3 springs, 1 plunger, and 1 trigger pin from a standard parts kit. I may change out the fancy pants mag release button for a regular mil spec one (not the ambi mag release). I did not put in the buffer retainer parts because I used the captured setup.

I do not trust the bathroom scale that I used to weigh it, but it claimed 4.6 pounds. I was expecting 5.5ish. The upper currently on it is aero slick side upper, Faxon midlength 14.5 pencil barrel with pinned and welded flash hider, geissele ambi charging handle, aero atlas one hand guard (I intend to switch this to carbon fiber and use it on the 605 upper), and sig Romeo 5. It feels very much like a toy.
been thinking about one of those lowers but figure I should hold off in case they're trash
have thrown away a hundred bucks on less before though

more on topic, also been meaning to put together a 605 clone, but middy gas and a full 16" barrel
as with all gun related projects lately, ain't got round to it
I do not trust the bathroom scale that I used to weigh it, but it claimed 4.6 pounds. I was expecting 5.5ish.

Do you have a trigger pull gauge? Mine goes from 0-15lbs (cant imagine a 15lb trigger) so I just hang the entire rifle off that to get an accurate weight.