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Posted: 1/23/2006 3:25:10 PM EDT
[Last Edit: 1/24/2006 5:42:16 AM EDT by idonutn0]
Whats the difference between Dissipated, Carbine, and Rifle length gas systems?
May be a silly question but all Ive ever messed with is a 20 in rifle.

Thanks in advance
Link Posted: 1/23/2006 5:22:00 PM EDT
The location of the gas port.

There are actually three different lengths in gas systems:

-Rifle length is what you see on the 20" AR's and is the longest distance between the chamber and the gas port. Approx 12"
-Carbine is the shortest. Approx 7"
-Midlength splits the difference. Approx 9"

Dissipator refers to a carbine length barrel (usually 16") with rifle length handguards. This dosen't always mean that it has a rifle length gas system as many Dissipators actually use the carbine length system with a low profile/cut down gas block under the hand guards.

Link Posted: 1/23/2006 5:55:21 PM EDT
Great question and a great answer.

I wan't sure myself and never got the nerve to ask.
Link Posted: 1/23/2006 8:13:05 PM EDT
[Last Edit: 1/23/2006 8:14:25 PM EDT by liquiddeputy]
I built this Dissipator kit last year--check out my rifle's barrel (click on the thumbnail photos):



The front sight in this application has no purpose in the gas system or in making the gun cycle; it's just a sight. (Normally, the front sight is ALSO the gas block, where the gas tube attaches, and blows gas back to your bolt carrier.) As you can see, my ACTUAL gas block is a cut-down sight that will go under the handguards. This gun is a Dissipator, but it runs on a carbine-length gas system.

Dissy's are cool because they provide a long sight radius on a 16" barrel, but they're heavy, and why I sold mine. FACTORY Dissy's use a CARBINE-LENGTH gas system when set up like this. People who make a Dissy from home from a 20" sometimes use the RIFLE LENGTH gas system, but you have to tweak it a bit to cycle well--usually, it means opening the gas port up (drilling).

Here's the same gun, done:


Now, compare that to my NEW carbine:

Same length barrel (16") AND gas system (carbine), but in this case, that sight IS also the gas block--accordingly, my sight radius on this gun is about 5" shorter than my Dissy was, but,... well, I like it a lot better because it's just a ton lighter!

Hope that helps.
Link Posted: 1/24/2006 3:27:53 AM EDT
These are great answers, thanks.
Ok, so does that mean that the terms, Carbine, Mid-length, Dissipator, and Rifle-Length ONLY deal with where the gas system cuts off at the gass block placement or is there more to the types/names then that?

Thanks agian.
Link Posted: 1/24/2006 11:02:26 AM EDT

Originally Posted By idonutn0:
These are great answers, thanks.
Ok, so does that mean that the terms, Carbine, Mid-length, Dissipator, and Rifle-Length ONLY deal with where the gas system cuts off at the gass block placement or is there more to the types/names then that?



That's pretty much it--they relate to your gas block and front sight placement down the barrel. Carbines have the ~7" gas system, Dissy's do too but have another front sight farther down; middy's have something like a 9" tube and midsize handguards on the same 16" barrel generally, and rifles (20 or 24") use the long 12" system.

Next week, we'll discuss how everyone built their SPRs (special purpose rifles) that can have a gas block in either position with FF tubes and flip up sights located anywhere, too!
Link Posted: 1/24/2006 12:21:16 PM EDT
Well, that clears it up for me. Just wanted to know the terms and definitions.
Thanks for all the help.
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