AR Sight radius

[halfmoonclip]

Got (used) a Brownells AR Carbine, 16" bbl, full sized handguards, so the front sight is only a short distance from the muzzle.
Some years ago, snagged one of those CHPS carbines that Colt made for the Cali Cops that would fit their existing shotgun racks. It, too, has full length handguards, and the sight close to the muzzle.
We'll ignore the gas system for the moment (the first is rifle length, the second carbine); my question is about sights.
When the platform was new, it was all about iron sights. Why was more effort not put into getting the front sight closer to the muzzle? Sight radius makes a huge difference in accuracy.
Why didn't the military consider a 'dissapator' style rifle, even for the 20" version?
Moon

 

[General Geoff]

No idea but I like dissipator rifles in concept; the execution is sometimes not all that reliable.

These days you can just get a mid length gas system rifle with a 'dummy' A2 gas block front sight out at the end of the muzzle.

 

[GunnyUSMC]

The original Dissipators were built by Bushmaster back in the late 80’s. They were built with heavy Bull barrels that stepped down at the front sight post.



It had the same gas system and sight radius as the M16A2. But the A2 barrels had a slim profile under the handguard. The A2’s barrel was heavier forward of the front sight base. It was said that it was for barrel harmonics.
The M16A2 was also designed to use a bayonet. If the front sight and handguard would have done like the Dissipator, a bayonet could not have been used.



Someone did make a bayonet for a Dissipator, but it looked silly. And wasn’t useful for anything else.


If I remember right, the Marine Corps used Dissipator uppers at some of the US Embassies.
The problem with the rifle gas system on a Dissipator came about when people started shooting non NATO 5.56 and 223 ammo.
The Dissipator was becoming very popular and to solve the ammo and feeding problems with it, manufacturers started offering carbine length gas systems barrels with a front sight mounted where a rifle front sight would be.




I shot one of the original heavy barrel Dissipators and will tell you, it was one smooth shooting carbine. The only problem was that it was heavy.
A friend of mine bought one of the Tiger McKee Katana carbines not long after they came out. It was a new twist on the Dissipator. It used a little profile barrel like the A2 under the handguard. After shooting it, I had to have one but wasn’t about to fork out the money they were asking for one.


So I bought an FN CHF barrel and had it cut and threatened at 16” and built my own. It shoots great with NATO 5.56 ammo. And it’s a smooth shooter too.

 

[halfmoonclip]

Wow, Gunny, not just an answer but an explanation, with great pictures. Thank you.
Some reflections
-Bayonet; point taken, and I thot about that; if you're down to bayonet and buttstrokes with an AR, you're really in the poo. The front sight simply could have been mounted on the end of a bare barrel as well.
-The heavy-barrel dissipator-like California Highway Patrol Carbine, AR6536, is indeed a smooth shooting carbine, but the HB makes it a tank. Do like that long sight radius for irons. These were apparently a run only for Cali, to fit the cruiser's existing shotgun racks, but there are some out there. It has the carbine gas system.
-The Brownells/NoDak carbine (RO605?) replica has that long sight radius, but, pencil barrel, so it's not heavy. It's also a rifle gas system, so there is a short barrel dwell time after the gas port. It was claimed that this replica has a bigger gas port to help compensate. Mine runs 100% with NATO 55 gr and Colt BCG. Function is hit-or-miss with a generic BCG, an event I can't explain. Gunny, you have a rifle system on that really handsome carbine; you said it runs well on NATO spec ammo only? Yours shares the 3-prong flash hider with the NoDak replica.
With optics, the ironsight issue is moot. Some of us still like the simplicity of irons.
Again, thanks guys.
Moon

 

[GunnyUSMC]

The Dissipators with the carbine gas system will function with just about any 5.56 or .223 ammo. This is because most are over gassed.
I’ve built two other Dissipators with the PSA med length gas system. Both guns functioned great with all the ammo we ran in them. They were smoother shooting then the one with a carbine gas system.
PSA still sells them for under $250 without a BCG.


I had a lot of fun building mine. When I had the barrel cut down, I was in my friend’s shop and watched him do the work. Here’s most of the parts just before I built it. I do like the old three prong flash hiders because, they work great and look cool.

 

[halfmoonclip]

The 16" retro carbine's function has been a mystery; posted a clumsy question here about it previously.
Always liked the looks, but didn't want to spend the money from Brownells. Found one sans BCG at a gunshow for something like $150; brought it home and stuck a generic BCG in it; it was not reliable.
The lower is part of a M16A1 replica I built, with a NOS Colt upper and BCG.
Put the Colt BCG in the retro 16" upper, and it ran just fine.
Stumbled across an SP1 (part circle) Colt BCG, and it runs just fine on that as well.
Go figure.
Moon

 

[GunnyUSMC]

I’ve got a BCG that will not run in one of my pistols. I tried three other BCG’s and the pistol ran fine. I put the BCG that would not run in the pistol into three different AR carbines and had no problems. I could never figure out why that BCG would not work in that pistol.

 

[halfmoonclip]

Okay, Gunny! LOL.
One of the few pearls of wisdom bestowed by my dad, "**** happens".
Sounds like this falls in that category.
Thnx for the education, be well.
Moon

 

[RevolvingGarbage]

I for one would like to make a custom gas block design to try out which pushes the front sight all the way out to just behind the flash hider on my 20” gun. Seems to me a pretty simple matter but I’ve never seen such a thing done anywhere. The 20” gun is going to have a long barrel so why waste possible sight radius?

 

[GunnyUSMC]

I for one would like to make a custom gas block design to try out which pushes the front sight all the way out to just behind the flash hider on my 20” gun. Seems to me a pretty simple matter but I’ve never seen such a thing done anywhere. The 20” gun is going to have a long barrel so why waste possible sight radius?

Just build a rifle with a free float rail. They now make hand rails that are 17” long.


You just mount your sights like this.

 

[RevolvingGarbage]

Just build a rifle with a free float rail. They now make hand rails that are 17” long.
View attachment 1059622

You just mount your sights like this.
View attachment 1059623

Certainly that’s an effective option. My rifle is set up with triangular handguards and I like them quite a bit. My idea was more to make a gas block which had a kind of boom running out along the barrel (in lieu of the A frame front sight post) ending in a front sight tower sticking straight up behind the flash hider.

Here’s a quick and dirty illustration to show the concept I had in mind. I flubbed the spacing with the barrel and the sizing versus the ghost A frame I drew but it shows roughly what I was picturing in my mind.

 

[General Geoff]

If you want the ultimate in sight radius, just pick up a Houle Bloop Tube and stick a precision sight atop it

 

[lysanderxiii]

Got (used) a Brownells AR Carbine, 16" bbl, full sized handguards, so the front sight is only a short distance from the muzzle.
Some years ago, snagged one of those CHPS carbines that Colt made for the Cali Cops that would fit their existing shotgun racks. It, too, has full length handguards, and the sight close to the muzzle.
We'll ignore the gas system for the moment (the first is rifle length, the second carbine); my question is about sights.
When the platform was new, it was all about iron sights. Why was more effort not put into getting the front sight closer to the muzzle? Sight radius makes a huge difference in accuracy.
Why didn't the military consider a 'dissapator' style rifle, even for the 20" version?
Moon

Front sight height.

The front sight on the M16 is pretty tall as it is. It would be rather fragile if it was another inch taller. Then there is the fact that it would way out at the end of the muzzle make a bunch of extra parts.

So why not move the gas block out there? Gas timing, and weight and balance.

 

[Bcwitt]

I think the front sight location was to enable the use of rifle grenades. A 22mm NATO slips right over the birdcage.

 

[Charlie98]

If I remember right, the Marine Corps used Dissipator uppers at some of the US Embassies.
The problem with the rifle gas system on a Dissipator came about when people started shooting non NATO 5.56 and 223 ammo.
The Dissipator was becoming very popular and to solve the ammo and feeding problems with it, manufacturers started offering carbine length gas systems barrels with a front sight mounted where a rifle front sight would be.

There was a USMC Dissy used in the first Jason Bourne movie, in the US Embassy scene. I thought it was pretty cool looking, and debated building one. I have since wised up and just stuck with mid-length systems for the 16"

What was the issue with problems? Because the gas port was so close to the muzzle?

 

[mjsdwash]

not sure the exact term, but many people cant focus on the target with longer site distance. I shoot 16" guns much better that 20".

Also, the shakier your hands, the more you benefit from a shorter distance. The A2 sight runs about 5oz total, and having that further out has its own issues.

They make bayonets unusable, and that certainly has military consequences.

 

[GunnyUSMC]

There was a USMC Dissy used in the first Jason Bourne movie, in the US Embassy scene. I thought it was pretty cool looking, and debated building one. I have since wised up and just stuck with mid-length systems for the 16"

What was the issue with problems? Because the gas port was so close to the muzzle?

A rifle gas system on a 16” barrel gives you a very short dwell time. It does make for a very smooth shooting carbine with standard NATO specs ammo. But there’s some ammo on the market listed as 5.56 NATO that is loaded to the velocity, but not the pressure. This has to do with the powder they use. And then there’s .223 Rem. ammo out there like PMC Bronze. It’s great ammo but it just doesn’t have the pressure to function 100% in my Dissipator. The problem is that it will short stroke. It will eject, but not feed another round from the magazine.
To get lower pressure ammo to function reliably in a Dissipator with a rifle system, you need a larger gas port. It’s an easy fix, but then the gun doesn’t run as smooth with NATO spec ammo.
The trade off is to go with a mid length gas system Dissipator upper like PSA sells. The mid length gas system will function great with .223 and 5.56 ammo.
The big plus to a Dissipator is ruggedness with a longer sight radius. Full length rails are great and have their advantages, but for fixed sights, a front sight tower pinned to a barrel is much stronger. And then there’s the fact that Dissipators just look cool.