Barrel-cut-down-question

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[ARCHIVED THREAD] - Barrel-cut-down-question

Posted: 1/19/2006 8:09:26 AM EDT

Hi,

here in Germany the barrel has to be 16,75 inch (42cm) for a sporting rifle.
This will include the chamber AND a fixed breake/comp.
So the gas system of most "short" AR´s here will be a midlength one.

What I like to know is...if I cut down the barrel by 2-4 inch will the middi gas system still work well ?
Cause I plan to cut down the barrel and get the legal-length back with a nice break or comp.

What are your experiance ?

Thanks

Posted: 1/19/2006 10:49:12 PM EDT

[#1]

Come on !!!!

Is there no one who can tell me if the Ar15 will still work error free if I cut down the barrel in front of the gassystem ????

Posted: 1/19/2006 10:56:16 PM EDT

[#2]

If you chop the barrel in front of the gas block it should work fine........as far as I know.

Posted: 1/20/2006 3:09:14 AM EDT

[#3]

...I saved this VERBATIM from a previous post. The Poster was asking whether it was possible to make a 13" length barrel with a midlength gas system.

There are two different questions or assumptions here...

If you want a mid-length handguard on a 13" barrel, that's no problem.
I would put a gas block at the carbine location and then a mid-length handguard that covers it.

If you want a 13" barrel with a mid-length gas system, now you are looking for trouble.

10.5" barrels with carbine-length gas systems are not known for their reliability with as wide a range of ammo as a similar 14.5" barrel would be reliable with.
This is due to the proximity of the gas port to the muzzle.
You need a certain amount of "dwell time" (for lack of a better term) where the gas enters the gas system while the bullet is still in the bore.

The mid-length specs basically call for moving the gas port 2" further forward.
That gets you the same gas system issues with a 13" mid-length that you have with an 11" carbine-length gas system barrel.

Typical 14.5" barrels with carbine gas systems have 6.7" of bore in front of the gas port.
20" rifle systems have 6.8"
16" barrels with carbine gas systems have 8.2" and mid-length 16" barrels would have 6.2"
It's a general guideline that you do not want to go much under 5" before reliability starts to suffer.
11.5" barrels with carbine gas systems have 3.7" in front of the gas port (seeing a pattern here yet?)
10.5" has 2.7" in front of the barrel.
The 14.5" mid-length barrel mentioned in another post above would have 4.7" which is about as short as you want to go.
Lastly, your theoretical 13" barrel with a carbine-length gas system and a mid-length handguard would have 5.2" and you are looking good.
Move that gas port out to mid-length and you only have 3.2", much less than optimum, but it could still be made to run.

Randall Rausch
www.ar15barrels.com

>I've heard that the military has had some success with 12.5 middies. YMMV.
>
>Dwell time isn't the only issue--a middie 13" would have a lesser peak presure, which is better.
>

I believe that you mean "port pressure", not "peak pressure".

The peak pressure happens in the first few inches of bullet travel.
Port pressure is what is unleashed into the gas system.
Port diameter is used to meter the gas so pressure is actually not as important as total volume that the system gets fed.
Having said that, the mid-length gas system is more gentle and the rifle system is even kinder to the action.
I still think that the 13" barrel and mid-length gas system is a step backwards in total reliability/versatility.

Randall Rausch
www.ar15barrels.com

Check out his site further, a lot of good technical infos on barrels.

Posted: 1/20/2006 4:18:18 AM EDT

[#4]

should as long as you open up the gas port to accomodate the shorter bbl.

Posted: 1/20/2006 6:04:30 AM EDT

[#5]

Thanks a lot for that link !!!!
Help´s me on my way.

Vielen Dank.

Posted: 1/20/2006 12:53:53 PM EDT

[#6]

I had a 20" barrel cut to 18" and it works perfectly without any other changes. VERY happy with it this length.

Posted: 1/20/2006 5:43:32 PM EDT

[#7]

I cut down a 20" barrel to 16.25" and it needed gas port opening to work.

Posted: 1/21/2006 2:29:57 AM EDT

[#8]

mid-length 16" barrels would have 6.2" It's a general guideline that you do not want to go much under 5" before reliability starts to suffer

So the barrels here would have about 7" after the gasport.....(legal overall 16.75" )
From what I read I could cut of 2" without any problem.

Now I just need to find a break/comp that is 2" long.

Thanks for your help.

Posted: 1/22/2006 10:32:40 PM EDT

[#9]

More here: www.ar15barrels.com/prod/gas-systems.shtml

Posted: 1/23/2006 6:42:56 AM EDT

[#10]

[ARCHIVED THREAD] - Barrel-cut-down-question

AR-15 » Rifles, Uppers, Lowers, Barrels, and more

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