What is an AR-15 Dissipator?

What the heck is an AR-15 Dissipator?

Fear not…

We’ll go over what makes an AR-15 dissipator, its pros/cons, and whether the design is still useful in this day and age.

Definition

Bushmaster Dissipator
Bushmaster Dissipator

A “dissipator” or “dissy” is an AR-15 with a 16″ barrel but with rifle length front sight post.  There’s some controversy about who invented what, but they can first be seen in Vietnam era photos.

Why?

The concept of the dissipator hinged on two positives:

  • A shorter barrel allows better maneuverability and weight savings
  • A longer sight radius allows for better accuracy

How?

Original designs were created simply by cutting down existing 20″ rifles down to 16″.  However, this led to reliability issues due to changes in the overall timing of the rifle.

Cutting down the extra four inches reduced the “dwell time” which is the amount of time the weapon maintains pressure so it can cycle.  You can think of it as the amount of time the bullet stays in the barrel after it passes the gas port.  In the dissipator barrel below, there’s almost no length left for the bullet after it passes the gas port which made the weapon unreliable.

AR-15 Gas Systems & Barrel Lengths
AR-15 Gas Systems & Barrel Lengths

Current Dissipators

Bushmaster Dissipator
Bushmaster Dissipator

Bushmaster came out with the first civilian AR-15’s actually called the Dissipator which had shaved-down gas blocks at the normal carbine length and then a “dummy” A2 sight block up in front at the rifle position.  They are still available and now dressed up to meet current trends of Magpul MOE furniture.

Bushmaster MOE Dissipator
Bushmaster MOE Dissipator

PSA also offers their mock version of the dissipator with a mid-length gas system.

PSA Dissipator
PSA Dissipator

However, there are still some “real” dissipators out there with enlarged gas ports and just one real front sight/gas block at the rifle position that have since solved the reliability issues.  Del-Ton ($430 upper) is the one that stands out.

Delton AR-15 Dissipator
Delton AR-15 Dissipator

Pros/Cons

We’ve already gone through the major pros with shorter barrels and a longer sight radius.

Some other advantages include a longer handguard which allows a more forward hand placement, protection from a hot barrel, and more space to accessorize.  And lastly, they bring an old-school kind of cool that resembles a short-barreled rifle (SBR) from far away.

Some of the cons include reliability and weight.

While reliability has mostly been fixed with gas blocks at carbine or mid-length positions, this adds additional weight from “dummy” gas blocks/sights at the front and longer handguards.  But, “real” dissipators with just one gas block at the rifle position also have fixed the weight issue with enlarged gas ports.

Is the Dissipator Still Useful?

With today’s free floating gas tubes and shift toward optics, does the dissipator still have a place?

Our answer is if you are ONLY going with iron sights.  Otherwise, there’s too many other options to get the same advantages of a shorter barrel and more accurate sights with reliable red dot and holographic sights.

Update: And check out the comments for some other points of view about the “dissy.”

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