Barrel extension problems

[Scoots]

To make a long story somewhat short, I brought in my AR to a dealer and we tried several bolts to find one that would headspace correctly - no luck. So I went back home and carefully examined the barrel and all components. The barrel's gas port is off several degrees from Top Dead Center with the upper receiver (funny I never noticed that )

To get the gas port to TDC the barrel extension will have to be tightened a few degrees, and that just may solve my headspace problems. What do you think? If the barrel extension can be corrected I will have to have someone do it for me - if that can be done. What do you think?

Next month will make a year on this project. It's been one headache after another. If I can't get this barrel extension problem corrected I'm going to start with a whole new barrel!!!

[DonT]

Scoots,

I have a few questions for you on your issue and it is my understanding that trying to "tighten" the extension a "few degrees" is virtually impossible and here is why. The extension is screwed to the barrel then it is pinned in place with the indexing pin. To move it just few degrees would mean you would be redrilling almost in the same hole and it would become elongated.

Here are some thoughts:
It is my understanding that the headspacing is done off the extension not the barrel as you find on other rifles. Also when the gas port it drilled it is usually in line with the indexing pin and the only way to tell if this is the case is to pull the barrel from the upper and look at it. What can typically happen is that where the barrel nut goes on the upper there is a slot that the indexing pin fits into. Sometimes these are a bit wider than they need to be allowing the barrel to twist (a few degrees, sound familar) when the barrel nut with the delta ring are tightened. This is easily fixed by someone with the correct tools and knowledge. It isn't necessarily a hard thing to fix depending on who put the upper together and if it was done correctly.

What are your headspacing issues? I may have missed them in an early post. Typically the bolt headspaces on the extension, at least that is my understanding. What kinds of problems are you having? Many times issues thought to be headspacing issue can be traced back to case length, seating depths, brass thickness, etc.

Please bear in mind I am not trying to say you don't have a headspacing issue as that would be pretty foolish on my part not having inspected the weapon. But it has been my experience that is usually is not the culprit.

If you want feel free to send me an email outlining the problems you are having and I will see if I can point you in the right direction. I am not an expert by any means but have 5 successful builds under my belt, one being a switch barrel gun that uses 4 different barrels (and calibers) with only 2 different bolts all in the same gun.

If you don't want to do that then I would suggest finding someone in your area that is very familiar with AR's. Not to knock anyone but a lot of shops or gunsmiths can be excellent with semi auto sporting guns or bolt actions and not be familar with some of the "fine points" (read as quirks) that are specific to AR's.

I am willing to try to help if you want it. No guarantees but I am pretty sure we should be able to point you in the right direction anyway...... I wish you were in the neighborhood I would have you bring it over and we could tear into it to see if we could get you up and running as I like a challenge..... Nobody should have to go thru the frustration for year just to be able to shoot their AR...

DonT

[tp555]

Yes I done lots of them.It is a pita but doable. How much is the gas port off?
Can you measure or guess? This will shorten your chamber. Worst case is to recut the end of the barrel by 1 thread about .060" then set everything else
up.Your gas tube might need to be cut but most gas tube specs give you some slack. I took oly 243 wssm"s and recut them to 6x45 with an intermediate gas tube and stock barrel ext's.Why? Because my customer said so.regards.

[Scoots]

DonT and tp555,

Thanks for replying to my post.

The bolt of my AR closes on my Pacific Tool and Gauge GO and NO GO gauges in 221 Fireball. I brought the AR to an Olympic Arms dealer and we tried out several different Oly bolts. All the bolts closed on the NO GO gauge. I figured this would be a good chance of correcting the headspace problem, as it is an Oly barrel, but no such luck.

After I brought the rifle home I took everything off the barrel, and that's when I noticed that the gas block was not correctly centered with the barrel indexing pin, the gas block was not correctly centered over the gas port, and that the gas port was about 5 degrees (maybe more) from Top Dead Center (not aligned with the barrel indexing pin) The indexing pin fits tightly into the slot on the AR upper.

I called Oly Arms and spoke with Andy, Oly's head gun tech. He gave me one more test to try - cut and place a piece of masking tape on the bottom of the No Go gauge. That will add about another .004" to the No Go gauge and make it the approximate equivalent of a Field Gauge. If the bolt still closes, then Oly wants me to ship the barrel back to them and they'll re-do the barrel for me, ensuring headspace is correct, and indexing pin and gas port are in alignment.

I'll keep you posted.

[pug]

Since it is a factory barrel then they will probably get it straight for you if needed. If the barrel maker sticks to using components that are in spec and puts the correct length shoulder for the extension then the headspace is only between the barrel and the bolt since the only variables left are chamber depth and bolt. A barrel for an AR is not a barrel until after the extension has been correctly installed. Then chambering process continues until the barrel correctly headspaces with a gauge and a particular bolt. Most AR barrel makers will not guarantee headspace unless you supply them with the bolt you are going to use. This doesn't help with your problem much but hope it helps explain a little. Andy is correct in it may be in field spec but if you can truly see the gas port is off by a bit you may want to send it back anyway as other little irritating problems come up when the port is off like low gas pressure or the gas key dragging on the tube if you align the port otherwise you have to custom bend the tube so everything works ok. Hope everything works out for you.

[tp555]

The bolt spec is + or - .001".Some mfg's cut the chamber final and screw on the ext.To check after the ext is on is extra work and not done.Thats the difference
between production work and one at a time.

[pug]

The tolerances are suppose to be quite tight but I have returned bolts that were almost .010" off. They were not cut deep enough though rather than too deep. Assemblers at the factory can swap and choose among parts to get a working combination rather than throw the out of spec parts out. I have had an out of spec carrier setting on the shelf forever because it was too big to fit in any of the uppers I used. Just the other day I picked up a used A2 receiver and bingo, the carrier fit perfect. Anther saved part :).

[Scoots]

Alright!!!

The masking tape on the base of the No Go gauge prevented the bolt from closing!!!

I used my calipers and measured the gas port placement from TDC with the indexing pin. It is only off a few degrees (according to my rough guestimates). I had enlarged the gas port to .109", maybe that will help with the gas block not being exactly centered over the gas port (couldn't get the gas tube to bend very easily, and I wasn't going to force it).

I'll have to try a few unprimed cartridges and see how well they feed from the magazine into the chamber. From there I'll see how the AR cycles with some subsonic rounds.

I'll keep you posted!

[pug]

Since you have unprimed cases then you must be handloading. Like 320pf mentioned in the other thread you can compensate for the extra headspace by not pushing the shoulder as far back. If its an Oly barrel it probably has a slight countersink to the gas port to compensate for misalignment any way. After the gas tube is assembled look inside the receiver and make sure it runs straight down the center of the receiver. This is where a slight cant to the gas block will be most noticed and if the tube is off center slightly use a big flat blade screwdriver to bend it to centerline (gently but firmly). This will prevent any drag to the gas key and premature wear.

[HotLead]

Scoots,

I didn't see any mention in either of your threads on your method of testing headspace.

I hope you are not closing the bolt on the headspacing guage like you are loading a round, or placing it in the chamber and closing the bolt. Even riding the bolt home with the guage in the chamber may give false results.

Someone please correct me if I am wrong, as I understand it, you are supposed to take the bolt out of the carrier, strip the ejector and extractor, and then reassemble the bolt back into the carrier. Then slowly reinsert the bolt/ carrier into the upper receiver and try to close the bolt with finger pressure only on the rear of the carrier. Excessive headspace will allow the bolt to cam into battery on the no-go guage, and the rear of the carrier will be flush with the receiver.

-JD