I am wanting to build a Dissapator upper, but I have been told that it is not a easy as cutting the barrel & re-threading for a flash hider. I have been told that the gas tube has to be reamed to a larger diameter, etc.... I am having trouble understanding how removing +/- 4" of barrel will effert the gas system, since the front tower & gas block hasn't been moved.  I can find a 20" upper without any trouble, but don't want to start a project that will not turn out like I want in the end. Any help would be great.

Thanks...

Quoted: I am wanting to build a Dissapator upper, but I have been told that it is not a easy as cutting the barrel & re-threading for a flash hider. I have been told that the gas tube port has to be reamed to a larger diameter, etc.... I am having trouble understanding how removing +/- 4" of barrel will effert the gas system, since the front tower & gas block hasn't been moved.  I can find a 20" upper without any trouble, but don't want to start a project that will not turn out like I want in the end. Any help would be great. Thanks...

Fix your post above.....

Shortening the barrel causes the bullet to exit the barrel quicker, meaning it directly affects the amount of "gas" traveling thru the "gas-port" (in the barrel) and into the gas-tube and on into the carrier key.

Mike

Many companies make what you describe, with a gas system in a similar location to a "shorty" handguard setup, and a dummy front sight with no gas going through it.

Unless you have some reason you want to do it yourself, just buy what you want from the factory.

If you must make it yourself, I'd probably start with a CAR barrel and go from there.

Of course, this probably will NOT be a "bolt-on" job.  Some fabrication required

check ar15barrels.com.  I'm sure randall can help if not he can give you some recommendations.