Also how big should the gas port be when the m4 barrel comes down to 11.5?  My reason for such work is that I need a Light gun for shortrange 3gun type matches. Also pictures of 11.5 barreled ar`s would be nice.

Couple of things to consider,

First, cutting back a chrome lined barrel is a big no-no. Chrome can start flaking resulting corrosion between the chrome and the barrel.

Second, do not tinker with the gas port UNLESS your rifle fails to feed and you can positively determine the reason. I have a 11.5" Commando (Cut back from 16")and it works fine without any alternations.

Hope this helps.

Best.

Petri

It is pretty common lately to cut back chrome lined barrels. I hear that if you're careful its not a problem.

Quoted: Couple of things to consider, First, cutting back a chrome lined barrel is a big no-no.

Ummm no its not.

Chrome can start flaking resulting corrosion between the chrome and the barrel.

Dude, where do you get this crap from?

Second, do not tinker with the gas port UNLESS your rifle fails to feed and you can positively determine the reason. I have a 11.5" Commando (Cut back from 16")and it works fine without any alternations.

Well there are specific dimensions for gas port sizes and why should he send the barrel off to get it chopped and threaded and not have the gas port checked to make sure it was not on the small size of normal and thus needs to be opened up?  The only issue I can see is the gas port will no longer be chorme lined if you do that.  And thats not THAT big a deal.

DevL, no need to be caustic about it, its something that a lot of people believe. An old rumor, I suppose.

Quoted: Quoted: The only issue I can see is the gas port will no longer be chorme lined if you do that.  And thats not THAT big a deal. Anyone know if the barrel is chromed after the gas port is drilled or before it is drilled?

Wild assed guess, but I seem to remember someone having a couple of NIW COLT barrels, never installed, with no FSB and NO gas port. This was in a post fairly recently. I THINK it was mongo, but not certain.

IF those barrels were chrome lined, that might be your answer.

Then on the other hand, I just might be sufferring a flashback to the 70's.



Lonny

Quoted: Quoted: Quoted: The only issue I can see is the gas port will no longer be chorme lined if you do that.  And thats not THAT big a deal. Anyone know if the barrel is chromed after the gas port is drilled or before it is drilled? Wild assed guess, but I seem to remember someone having a couple of NIW COLT barrels, never installed, with no FSB and NO gas port. This was in a post fairly recently. I THINK it was mongo, but not certain. IF those barrels were chrome lined, that might be your answer. Then on the other hand, I just might be sufferring a flashback to the 70's. Lonny

That's my barrel.  Here's my link:  Odd Colt Barrel

I don't think that it is a good idea to be drilling through the chrome lining of a barrel, so I would think that you would drill before the chrome lining.  I just don't know.  Shortening and crowning a chrome lined barrel has been done many times without issue, so maybe you can drill through the lining without issue.

For alot of short barrel issues, see the following link:  SBR Problems & Solutions

The hole is drilled and then its chromed.  When you pull your FSB you can see the chrome at the edges of the hole.  Then again I only saw this personally once and it could vary by manufacturer.

I would not cut a 14.5" bbl to get an 11.5.  There's enough of a market for 14.5's, that you could sell it and buy a new 11.5".  You're gonna need an SBR stamp anyway, so I see no problem buying the 11.5.  

In addition, I can't imagine a 3GM where an 11.5 would offer advantages that wouldn't be off-set by the need for a longer bbl in other stages.  Just my $.02.    

Finn
Member
Joined :: September 2003
Post Number :: 22

FIN

SBR? Finland is almost enlightened

Luck
Alac

There's no problem with cutting, or drilling, a chromelined barrel, lots of members here (including me) have had it done. However, the only thing that makes a M4 barrel a M4 barrel is the M203 cut on the front, and if you cut that off, then you won't really have an M4 barrel, anymore.

Quoted: My reason for such work is that I need a Light gun for shortrange 3gun type matches.

You may want to check if you have a minimum power factor for your 3-gun matches.  

Its my understanding (as a very junior 3-gun shooter) here in the states under USPSA/IPSC rules I have to be careful re: certain ammo manufactureres/ load combinations with my 16" barreled AR, or I might not even make Minor power factor with 55 gr. ammo. (Remington yellow box 55 gr. fmj's for one)


Also the minimum size for a 11.5 barrel gas port is .086 (.086-.094), which is the max port size for a 14.5 (.070-.086), so that may be ok.  Only one way to know for sure...

Trying to help.

Cheers, Otto

I have three 11.5" cut down M4 barrels and they work great.  Heck, the upper on my M16 in my avatar is one of them.  CMMG or ADCO are more than capable of doing the work for ya.

Here is another FIN opinion.
Cutting chrome lined barrel is NO PROBLEM
I have 20" Colt barrel and it was shortened to 18"

Gas hole might be too small after shortening barrel for proper funtionality.
I have also 11" barreled version with 2.6 mm diameter gas hole.
Here is the picture of the upper. It runs like champ now.
http://www.takkumaki.net/images/Colt1.jpg

Here is video showing how it runs:
11" Video

Quoted: I have three 11.5" cut down M4 barrels and they work great.  Heck, the upper on my M16 in my avatar is one of them.  CMMG or ADCO are more than capable of doing the work for ya.

Unsure of the difficulties of shipping that into/out of USA. One of the reasons he is looking to cut down his 14.5 may be difficulty securing parts.  ITAR muddles things. Hows the availibilty of stuff in Finland now? Maybe Finn can comment on motivation.

Anteeksi en puhu suomea

Luck
Alac

My reason is that I want a light and handy gun, the 11.5`s I`ve seen have been heavy barrels, m4 profile is light under the handguard.

The barrel came from USA a week ago and I have the capability to cut /drill it myself, just wanted to  know the gasport size.

No power factor in our  reservist shootings ( only a few IPSC Rifle matches per year, and for those I have a fluted heavy barreled 16" barrel)

Ok I will wade out into this one, and give my suggestions

I have had several discussions in relation to the issue of burning out gas ports etc and the comments have always been to the effect that if the gas port area could be chromed the problem would be eliminated, therefore and I do not manufacture barrels, I believe the process is to make the barrel, cut the chamber, chrome line it and then drill the gas port.

I am currently running, full auto, both a M4 profile and a 11.5 from CMMG, when I purchased them they stated that they cut the M4 down to the 11.5 to meet my specs.  Therefore I see no problem in having a barrel cut from a M4 (with the reduced size and weight under the handguard) to 11.5, not a lot of weight savings with a ll.5 granted.  I would call John at CMMG and ask him, take up 2 minutes of his time and then make a concerted effort to buy from him in the future.  He certainly deserves it as he delivers exactly what he says he can and it is always at the forefront of the industry.

I would not mess with the gas port to begin with, load a single round in a mag, fire it and see if it locks open on the empty mag.  If not that is a gas issue and further research as to the proper size hole is warranted.  You could even chance it by moving up one size drill bit at a time.  Again probably won’t even be an issue.

For what you are attempting to accomplish, I believe it to be a completely acceptable risk, however for what it’s worth I would buy an 11.5 and have both barrels at the end.  When you consider your cost of labor for the time spent it’s probably cheaper and gives you the option to backstep.  If you play with AR’s any amount of time you know how often we change out stuff and then latter go back to a previous configuration that’s why we shoot ar-15.

Good luck, with your project