What's a Dissipator?
The Dissipator concept came about briefly during America's involvement in Vietnam. Early slab-sided Colt 601 AR-15s, Colt 602 XM-16s, Colt 604 M16s, and forward-assist equipped Colt 603 M16A1s all had full-length 20-inch barrels with a good portion of that being past the gas block/forward sight assembly.
Troops in tight situations, such as crammed into helicopters and pushing through triple canopy jungle, found themselves wanting something handier. This led to a "field modification," which saw some simply hacksaw a few inches off the barrel to make the rifle shorter. This mod even became semi-official, with in-country workshops whittling down the barrel a couple of inches and then threading the muzzle to attach the flash hider.
The hacked Dissipator was born – although there is no evidence that it was ever called this in military service. The mod made the 6.5-pound early M16 more compatible in overall length to the 35-inch long M1 Carbines which, while not in U.S. frontline service at the time, were often "acquired" from local South Vietnamese troops due to their ease of carry.
The unwelcome news was that the Dissipator mod killed the rifle's dwell time and made a gun that was already of questionable reliability at the time even more prone to fail. Doh.
Colt even made the Dissipator concept refined with the Model 605, which included a bayonet-lug-less 15-inch barrel whose flash hider started right where the front sight assembly ended and a full-sized fixed buttstock and a rifle-length gas system. However, it was very soon superseded by the Colt 610/XM177/GAU-5A, which entered service by the late 1960s. With its adjustable two-position buttstock and a 10-inch barrel with a carbine-length gas system, it only took up about 28 inches of real estate and would go on to be the go-to shorty M16 for generations.
While the military walked away from the Model 605, it turned out the concept of an AR-15 platform with a full-length fixed buttstock and handguards with a rifle-length gas system on a trimmed-down barrel made for a smooth-shooting rifle while still coming in (a little) shorter than a traditional 20-inch full-length rifle.
A niche for sure, but one that black rifle makers took a chance on over the years with Adams Arms, ASA, Bushmaster, Delton, Doublestar, KAK, PSA, and Windham Weaponry all selling their own assorted takes on a Dissipator for the commercial market. The thing is, most of these are "mock" Dissipators, as they actually used carbine or mid-length gas systems with a low-profile gas block under the handguard. The A2 sight was pushed out as far as possible to give the short look of the Dissy while getting away from the old dwell time issue the Vietnam-era guns suffered from (more on this later).
The latest Dissipator comes from Anderson, which is why you’re here.
Overview
Truman Brough, Anderson Manufacturing’s Product Engineer, explained to Guns.com that the company's take on the Dissipator, which is based on its prolific AM-15 platform, is more modern than the field-hacked A1 style Dissy or its factory 605 follow-on.
The result looks like an M16A4 that someone chopped the last 4 inches of the barrel, threaded the new muzzle, and attached the A2 flash hider to the stump. In short, a Fallujah-era Dissipator rather than one from the Hue-era.
A handy rifle, it runs 35.5 inches long, about the same length as an M1 Carbine, and weighs 6.5 pounds while still having a 16-inch barrel, fixed stock, and a rifle-length gas system.
"This rifle answers the question: ‘What would have happened if the original chopped M16 made it all the way to the A4 generation?’” said Brough.
Further, it is a "real" Dissy, as it has the soft-shooting rifle-length gas system with a 16-inch barrel, not a "mock" Dissy lookalike as often marketed by other black rifle makers over the years.
For full disclosure, Anderson supplied Guns.com with this rifle for T&E purposes and all testing was done on this one gun.
The Specs
- Barrel: 16 inches, 1:8 RH twist, nitride-coated 4150 CMV, government profile
- Overall length: 35.5 inches
- Weight (unloaded, sans optics): 6.5 pounds.
- BCG: 9310 steel bolt, 8620 steel carrier, M16 profile
- Handguard: 12-inch clamshell with heat insulators
- Gas system: Direct impingement rifle-length gas system, A2 assembly .750-inch gas block
- Mag capacity: 30-round standard (one mag included)
Features
Taking a closer look at the Anderson A4 Dissipator, it uses a nitrided M16 profile bolt carrier group with an 8620 carrier and a 9310 bolt.
Trigger
The Dissy uses the company's Premium lower parts kit with a stainless-steel single-stage trigger and hammer. It is kinda gritty, but you can forgive it due to the sub-$600 cost of the entire rifle. We found it to break at an average of 7 pounds, which falls squarely into the typical "mil-spec" range of 5.5-to-8.5 pounds. It works.
Reliability
Military Dissys and the Colt 605 didn't work due to dwell time issues. On a gas-powered gun, running out of gas before the action cycles is usually a bad thing.
Generally, the way that manufacturers have made commercial Dissipator-length ARs to work, as mentioned above, is that they faked it and used an A2 sight but hid a low-profile mid-length or carbine-length gas system under the GI-style clamshell handguards. For that, it typically costs about $1K.
What Anderson did (and for closer to $600) is opt for a rifle-length gas system that actually uses the A2 sight as a gas block but opened the gas port massively to .110, which is even bigger than the typical 0.098-0.0935 seen on 20-inch rifles, to capture that gas pressure before it escapes.
The verdict? It works. We ran 500 rounds through it using a dozen different loads from 55 to 77 grains in several different styles of AR mags with zero malfunctions although we did note that it got filthy in that period. The bulk of that was Federal's American Eagle 55-grain FMJ. It ejected consistently at about the 3:30-4:00 position, which many consider to be a perfect ejection pattern.
Keep it clean and lubed, especially if going to a high round count, and make sure that BCG is good to go.
One thing when it came to cycling is the smoothness of the recoil impulse and absence of muzzle rise. It felt more like a 20-inch rifle with a decent muzzle break than a 16-inch carbine with the simplest flash hider known to man.
Accuracy
Between the long 20-inch sight radius, easy recoil impulse, and the decent trigger, we found the Anderson A4 Dissipator capable of meeting practical accuracy expectations. Without mounting optics or better sights, we zeroed in the rifle with the first gen MBUS rear – which needed several clicks left to meet the point of aim – and A2 front sight from a sandbagged bench at 36 yards, then verified it at 100. Using basic ammo – Federal's American Eagle red box 55-grain – we were able to run about a 1.5-inch MOA at 100 yards when using a death grip on the gun to avoid flyers.
Pros & Cons
PROS
- A Dissipator that works.
- Smooth firing
- Low cost
- Lots of easily replaceable A2 pattern parts
- Classic late 1990s/early 2000s styling
CONS
- No carry handle.
- The retro styling means no QD cups or M-LOK slots.
-
The bayonet gang may be upset.
Conclusion
Anderson's A4 Dissipator is a concept gun that never was as the military's flirtation with the Dissy concept was short and ended in a bad break-up. Black rifle makers defined just what a Dissy was, but the thing is, they all kind of had a different take on it. Anderson is doing it right in the respect that this one runs and feels great while doing it.
When it comes to rocks, some folks will probably complain that it doesn't ship with a carry handle – even if it is detachable – for the period drip. Then, when it comes to guys who want to add all sorts of stuff to it, the GI clamshells are going to disappoint but they can always be swapped out for a more modern quad rail or M-LOK handguard. The same thing can be said about the trigger. Either way, don't touch the gas system, as it works and works very well.
