why does a dissipator barrel need the gas port in the middle??

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[ARCHIVED THREAD] - why does a dissipator barrel need the gas port in the middle??

Posted: 7/19/2008 8:45:52 PM EDT

i was looking at the bushmaster catalog and the gas port is in the middle of the barrel. i though the dissipator barrel was just a 16" A2 barrel.

So why the gs port in the middle and difference between it and a A2 barrel??

Posted: 7/19/2008 8:50:17 PM EDT

[#1]

It's basically a carbine barrel with the front sight pushed up to the flash hider and full size rifle handguards. The gas system still needs to be setup like a normal 16" carbine to function properly.

Posted: 7/19/2008 11:10:03 PM EDT

[#2]

See above.

Posted: 7/20/2008 3:03:15 AM EDT

[#3]

Quoted:
It's basically a carbine barrel with the front sight pushed up to the flash hider and full size rifle handguards. The gas system still needs to be setup like a normal 16" carbine to function properly.

And to have the gas port thru the front sight base area would require a special length gas tube.

Posted: 7/20/2008 4:24:44 AM EDT

[#4]

Quoted:

Quoted:
It's basically a carbine barrel with the front sight pushed up to the flash hider and full size rifle handguards. The gas system still needs to be setup like a normal 16" carbine to function properly.

And to have the gas port thru the front sight base area would require a special length gas tube.

Well, if they had the functional gas block at the FSB they'd just be using a rifle length gas tube. No need for a "special length". They use the carbine gas system so they can have functional cycling (dwell time and all that). The point behind the dissipator is to have a rifle-length sight base on a 16" barrel. I used to think they were the cat's meow but now I'm "meh..."

Posted: 7/20/2008 6:56:02 AM EDT

[#5]

Quoted:
i was looking at the bushmaster catalog and the gas port is in the middle of the barrel. i though the dissipator barrel was just a 16" A2 barrel.

So why the gs port in the middle and difference between it and a A2 barrel??

+2 to what LAFPOL2 said. As far as your assumption, there are plenty of rifle length 20" barrels that have been cut back to make a dissy out there too that retain the rifle length gas system.

Posted: 7/20/2008 7:42:39 AM EDT

[#6]

Quoted:

Quoted:
i was looking at the bushmaster catalog and the gas port is in the middle of the barrel. i though the dissipator barrel was just a 16" A2 barrel.

So why the gs port in the middle and difference between it and a A2 barrel??

+2 to what LAFPOL2 said. As far as your assumption, there are plenty of rifle length 20" barrels that have been cut back to make a dissy out there too that retain the rifle length gas system.

Anyone here of relibilty issues with that set up? I would think it may be a bit ammo picky.

Posted: 7/20/2008 8:04:06 AM EDT

[#7]

height=8

Quoted:
+2 to what LAFPOL2 said. As far as your assumption, there are plenty of rifle length 20" barrels that have been cut back to make a dissy out there too that retain the rifle length gas system.

Don't forget CMMG's M10R; it's got the rifle-length gas.

Posted: 7/20/2008 9:47:38 AM EDT

[#8]

Quoted:

Quoted:
i was looking at the bushmaster catalog and the gas port is in the middle of the barrel. i though the dissipator barrel was just a 16" A2 barrel.

So why the gs port in the middle and difference between it and a A2 barrel??

+2 to what LAFPOL2 said. As far as your assumption, there are plenty of rifle length 20" barrels that have been cut back to make a dissy out there too that retain the rifle length gas system.

Thats exactly what I am trying to figure out. Does cutting a 20" barrel back to 16 really affect functioning that much??

Posted: 7/20/2008 10:02:41 AM EDT

[#9]

Yes. Rifle length gas system on a 16" barrel is not a good system. I suppose the port could be opened, but this gets tricky.

Posted: 7/20/2008 10:05:41 AM EDT

[#10]

If you want to start with a 20“ barrel you could cut it back to 16“ and open up the gas port or use a slightly longer barrel (17”-18“).
The easiest way is to use a mid-length gas system with the 16” barrel and mount the front sight in front of the gas block. This configuration should be more reliable than a rifle length gas system with the 16” barrel under adverse conditions.

Posted: 7/20/2008 2:22:56 PM EDT

[#11]

The term "Dissipator" is generally used to refer to a rifle that has the gas block behind the front sight.

The "Aardvark" puts the gas block in front of the front sight.

The rifle length gas system on a 16" barrel has been proven over and over (I tested it more than 20 years ago) to not be reliable enough for a service weapon.

A carbine that uses a rifle profile hand guards and sight placement, with a mid length gas system, is perhaps one of the handiest rifles you can find -- Not sure what to call it, Middipater? Anyway, I like mine a lot.

Posted: 7/20/2008 2:27:29 PM EDT

[#12]

The reason I was told is that the action needs x amount of gas to correctly cycle; to ensure this there needs to be four inches or so of barrel travel after the gas port to bleed off enough to function.

Posted: 7/20/2008 5:02:31 PM EDT

[#13]

Quoted:
The reason I was told is that the action needs x amount of gas to correctly cycle; to ensure this there needs to be four inches or so of barrel travel after the gas port to bleed off enough to function.

The three important parts of the equation are the total volume of gas generated while the bullet is still in the barrel, the amount of time between the bullet passing the gas port and exiting the barrel (dwell), and the size of the gas port. There are several examples out there of 16" barrels that run fine w/ a rifle gas system and an enlarged gas port, but they are the exception rather than the rule. With mid-length and carbine gas systems available why take the chances w/ reliability?

[ARCHIVED THREAD] - why does a dissipator barrel need the gas port in the middle??

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