The Story

What is a Dissipator?

A Dissipator is an AR15 carbine with rifle length sight radius.

The Model 605 was the first attempt by Colt to produce a "Carbine" style AR15/M16. The two models offered were the Model 605A which had a 3-Way Fire Control Group (Safe, Semi, Auto), and the 605B which had a 4-Way Fire Control Group (Safe, Semi, Burst, Auto).The barrel was cutoff just past the Front Sight Base, the Bayonet Lug was removed, and the flash hider was reattached giving the ‘Carbine’ an overall length of approximately 34 inches. This model was produced in very limited numbers and never saw any wide scale use in the field by Military Forces due to its unreliable operation.

Most call a carbine barrel with rifle length gas system and fixed rifle length FSB a “true dissipator” because that’s how Colt did the Model 605. The Model 605 was a standard 20 inch barrel cut so the thread shoulder was at the FSB, which came out to about 15”.

Bushmaster invented the “Dissipator” name in the ‘90s, and their barrel was a 16” Heavy Barrel M4 with carbine gas system hidden under the handguard with a rifle FSB. Some now call a non-rifle gas system, carbine barrel with rifle FSB a “Faux Dissipator.”

A rifle length gas on a 16” barrel needs to have a very large gas port to operate because of decreased dwell time. This makes the reliability very sensitive to changes in ammo and especially when used with and without a suppressor. The large gas port also accelerates wear and this diminishes barrel life. Colt did not continue the 605 system because it was not a reliable design.

Why build one?

Well usually the first reason for building a retro rifle is cost because you can typically save a few hundred dollars building your own. However this type of rifle is no longer being produced, Anderson Manufacturing was making their own version of a M4/A4 Dissipator but they are no longer in business, R.I.P. Brownells was producing 605 style clones but have not produced any in some time. TNTE produces ‘True Dissipator’ barrels and PSA sells a ‘Faux Dissipator’ upper receiver with a midlegnth gas system.

Ente built his Dissipator for around $1,000 USD with new & reproduction parts.

(Tools not included in that price.)

How did he do it?

Ente decided that the midlength gas system would be more reliable and went with Palmetto State Armory’s Dissipator Upper to rob the barrel and gas system to install on a Harrington & Richardson M16 ‘Slickside’ Upper reciever because Retro Rifles are just plain cool. Also A1 carry handles are Ente’s favorite upper receiver so we’re building an A1 dissipator. While he was getting parts from PSA Ente also picked up a PSA Stealth Lower, H&R Ejection Port Cover Assembly, Toolcraft Bolt Carrier Group, a Milspec Charging handle and a Luth AR Buffer Assembly.

Ente then went to Linemount for the furniture and the muzzle device. He got the A1 Handguards, Stock, Pistol Grip and a 3 Prong Duckbill Flash hider. He then went to AS Designs to get their ARC Fire active safety fire control group. To finish the build off he got a KAK M16 Lower Parts Kit and a Duramag 20 Round Magazine.

Upper Receiver Harrington & Richardson $140

A1 Sight Assembly Luth AR $19

Ejection Port Cover Harrington & Richardson $24

Barrel Palmetto State Armory $230

Handguard Linemount $25

Muzzle Device Linemount $40

Bolt Carrier Group Toolcraft $80

Charging Handle Palmetto State Armory $10

Lower Receiver Palmetto State Armory $50

Fire Control Group AS Designs $225

Lower Parts Kit KAK Industry $28

Pistol Grip Linemount $9

Pistol Grip Plug MLLL $5

Stock Linemount $80

Buffer Assembly Luth AR $53

Magazine Duramag $30

Total: $1,018

After it was completed he used headspace gauges to check the chamber clearance to ensure the rifle was safe to operate.

Accessories

Ente wanted to slap a sling on the rifle and used a M1 USGI seatbelt sling in OD Green to carry the rifle during training and hiking.

Sling USGI M1 Sling $20

After a few months of research, careful planning, sourcing parts and tools, the build was finished.

A list of parts and tools used can be found below. For those who want to build their own CAR-15.

Thank you for reading if you made it this far!

-Ente & Maltz

Founders of Functional Reserve Militia