Quick question, is there anything special about installing a barrel extension and the pin?  From the TM's it looks like you just screw it on and put the pin in?  I don't have the extension yet, so I can't visual it.

Any ideas?

Thanks,

Go to [url=http://www.brownells.com/aspx/NS/store/ProductDetail.aspx?p=12729&s=30794#30794]Brownell's[/url] and get the tools and a good torque wrench.

If this is going on a barrel which has had an extension previously installed, you might have a problem getting the new extension to index with the gas port, etc. Better not pitch the old one till you see how the new one fits.

Why have you found it necessary to change the extension on your barrel??

Actually, I got a like new barrel from someone but it only had the front sight assembly and that's it.  No barrel ext, delta rings, springs, barrel nut, etc.  So I had to replace the missing parts.  I might just let my local gunsmith install the all the stuff and attach the barrel to my upper receiver since I don't have any of the tools for this task.  Still working on my first AR.

Thanks everyone for the advice, but keep it coming if you have more.

Well, I've scratch built all my AR's, but I haven't scratch built a barrel assembly! For a first one, you're starting pretty deep.[;)]

Since you don't yet have the extension,you might try contacting Jeff or John at [url=cmmginc.com]CMMG[/url] and see if they still have any of the DPMS extensions with the M4 feed ramps, if your building that kind of project.

To install the extension you will require an extension tool(about $50) or the very minmum an old bolt modified for a socket(Welded to an impact socket).A torque wrench that reads 150lbs is also required.First snug the extension down tight a few times to engage the mating surfaces cleanly,then final tighten to 150ft/lb.Set up the assy in a drill press, preferably on V blocks and plate, and clamp so that the index pin hole in the extension is vertical.Drill pin hole 0.125" diameter at least 0.10" deep into barrel thread and fit pin.Pin should protrude sufficiently to engage upper receiver slot and not interfere with the threads on the receiver.Without unclamping/ removing barrel assy, slide setup along the press and drill gas port same size as original(check with # drills),the same distance from the handguard ring shoulder on the barrel,this will ensure that the gas port is indexed with the pin.Set up the drill press to drill only the depth required to enter the bore and no more.
With a bit of luck the holes will be far enough out not to interfere with the originals.Block the old gas port with a taper pin filed flush to the sight mounting surface and cut short enough not to protude into the barrel.The sight post will hold it in place without welding.
Check your headspace to ensure correct and sufficient,then run a lap up the barrel to remove possible burrs from the gas port hole inside the barrel and then clean and reassemble.
It's as easy as that!

IIRC, the barrel thread are not indexed like a a Garand or a FAL.  Getting a barrel extension to match up would be purely luck of the draw.

I would take a pass unless I found out otherwise.  This barrel sounds like a money pit if these threads are not indexed.  

You can buy new barrels with the extension in place pretty cheap.  I bought a couple from Northridge for what, 55 bucks apiece?  They needed a gas hole drilled, but that is easy to do.

Paying someone to do this work sounds expensive.  It would be where I live.  

Pogo said to weld a bolt into a socket to remove the extension.

Well, I did just that. My torque wrench is a CP and developes LOTs of torque.

I have an old de'milled barrel that I wanted the extension off of. So I put the barrel in my vise and hit it with my new handy-dandy tool.  I turned the barrel in the vise.  So I tightened it more.  Still turned.  So I TIGHTENED IT.  Still turned.  I then used an 18 inch pipe to tighten the vise.  Still turned.

So I laid a bead of weld on the barrel and hit it again. It didn't turn but wouldn't come off. So I increased the air to 180 PSI.  I then broke my tool.  Twisted the neck of the bolt off.  It was U-U-U-Ugly !

So next I put the assembly in my lathe and turned some of the barrel off to relieve the pressure from the extension. I figured that I could now use a pipe wrench on the barrel while it was still in the lathe chuck. It spun in the 3-jaw chuck. Again, I TIGHTENED it !  Still spun.


damn.   At this point, I think I have a good fishing weight for mackrel.

Roger

I said what?

That indexing pin on the old barrel extension should be drilled into the barrel.  That how I would install one in my barrel.  Not depth in a barrel extension otherwise for this large of a pin.

You would have to remove this pin or drill it out to have a prayer of removing the old extension.

You can buy a new barrel extension for less than 20 bucks, IIRC.

EDIT:  Those barrel extensions you buy from DPMS or whoever have a hole where the pin goes.  

One guy posted his barreling procedure a while ago.  Sounds pretty slick.

First of all, he faces off the rear of the barrel.

Then, he threaded the exterior of the barrel to fit the extension leaving the shoulder proud, say, 0.020" (my number).

He ran a chambering reamer into the barrel and used the bolt he was going to mate to THAT barrel, leaving a bolt/barrel gap of about .002-.003 or so with a headspace gage.

He then finished turned the shoulder using a off-the-shelf barrel extension with THAT bolt and headspace gage.  At this point, I ASSUME he would drill into the side of the barrel and fix the extension using the barrel index pin.  

I got a stripped used COLT 1/7 20" barrel for next to nothing, so I could build a good varmit/sniper rifle. After talking to my local smith, the money and time that he and I would have to invest to get it indexed, headspaced, and the gas port aligned and drilled would have been enough for a couple of new match barrels from any of the current makers.

My advice, unless restoring a collectors item or you own a machine shop with plenty of time to dedicate on the old barrel, give it up. Buy new. You will like the results more

i have an unused barrel extension wrench. i paid $45 from dpms for it i'll sell it for $30 plus $3.85 shipping.

I'm with TAC40--this isn't a project for anyone building their first AR. Trust me--you'll be much happier if you sell this barrel for whatever you can get for it, and get one with the gas port drilled and barrel extension already installed.

I wouldn't even consider indexing a barrel extension even though I've built several AR's and have all the tools--including a brand new, never used, barrel extension wrench that I bought from someone else for next to nothing because he never used it either.

I just have to ask, did you remember to take the pin out? [;D]

The original posting was for instructions to install an extension on a stripped barrel,and not removal.                                  To remove an extension,run a file over the extension pin to remove any turning hi spots or parting off points, this will enable you to properly centremark the pin.Drill the pin 0.125" or slighlty less to allow for  off centre drilling(the remainder of the pin will shear whilst undoing the extension),to the depth of the barrel extension thread core and no more (about 0.125" or so, below the ground outer surface of the barrel extension).Remove from the drill press and using barrel clamping blocks or soft jaws in a vice, and a breaker bar with your extension tool, remove the extension anticlockwise from the barrel whilst applying a little heat from a propane torch to the extension.Unless you have not drilled out the pin or the barrel has corroded into one solid mass,the extension should come off quite easily without resorting to the drastic and "ugly" measures posted above.  

A couple of useful pieces of info.
The lenght of the threaded portion of a new barrel without extension should be 0.620".
Headspacing should be done after the extension is torqued and pinned in place.
An increase in headspace is normally due to extension wear (at the rear face of the lugs)or bolt wear (the same place) and not normally in the chamber itself.
If the barrel bore itself is not 'shot out',then the procedure of changing the extension can usually rescue a perfectly serviceable barrel for around $15-$20.

Sorry for the confusion I may have caused.  The exact story is that I bought a colt barrel off of someone for a close to nothing price.  This barrel came off of a Colt HBAR Sporter.  For some strange reason, he already parted out the barrel nut, barrel extension, delta rings, springs, etc.  The gas port has been drilled and the front sight assembly is already on.

I thought at the time, oh well, I'll just go out and purchase all those parts and put them back on.  When I goto the extension, I said, ok, now what.


I have done business with GPSS in the past for a lower parts kit, so I called Tommy Haskins for a quote to install the parts.  So I will be sending this out to him and I'll post pictures of the finished products.

Thanks again everyone.  Maybe if I had more experence, I might have tried to pin it myself, but for 30 or so bucks, why not have him do it and head space it too.  Now if he calls back and says it's going to cost more for additional work, this barrel will be going on the EE fast.

Note to self: Do not buy Colt sporter Hbar barrel from sterling 18.  [smoke]