Any magic to an AR barrel extension?

[LVLAaron]

Sad No. In order for all of us to thrive there has to be rules. The rules are pretty simple and easy to comply with. I've never had an issue with ATF.

I love the government. I'm only sad because it delayed us learning trade secrets.

 

[Randfal]

Still have never seen anyone ever post their procedure on how they time their hole to the center of a groove. Let alone someone saying it was so simple that it was economical to do on any scale. I’ve bore scoped many high end AR barrels and can’t remember ever seeing any done centered up. Still waiting to hear what the “super easy Indian trick” is. Would love to know. Maybe it’s a “special tool” or test indicator with a 10” long stem lol.
Serious though, would love to see it written in black a white l, right here on this forum in front of the many good smiths that like to browse these pages. Also, with a picture(so easy and common that there’s gotta be pictures of doing it somewhere)heavy sarcasm.

 

[Aaron23]

It's probably not so much that it's hard, it's that it takes more time. Time to make a tool and the time it takes to use it. Same indexing a fluted barrel. It takes time.

You nailed it.

 

[DaveTooley]

It takes less time than a piss break. Of course that's age dependent. I'll get something up today. The morning is full right now.

 

[DaveTooley]

OK here goes.
The process then pics.

Completely machine tenon.
Screw extension on and mark the barrel top dead center using the locating pin. See pic. This is your starting point.
Set indexing fixture for the length from the shoulder to the gas port.
Run indexing fixture in to see where you have to go. Make a second mark. This determines the amount of rotation need for proper indexing.
Back the extension off a bit and face the barrel shoulder off until you have about an 1/8th of an inch left to rotate.
I use a grooving tool to cut all my shoulders, Better finish which adds predictability to the rotation. The other variable is the quality of the extension. All extensions go into the parts washer and get cleaned with a wire brush to remove debris from the threads.
After facing the shoulder and adjusting the rotation set your digital readout to zero or use a 2" travel indicator. Run the carriage back to the tenon length and face to length. That is never more than .010" at most unless you over shoot the mark.
Proceed with chambering and any other work on the end of the tenon.
Next turn gas port area to diameter and the shoulder to the correct location.


You have to do multiple operations when making the fixtures so all indicating surfaces are in alignment.
Example the flat on the rod for the cup has to be indexed with the center drill dot on the front end. Same with the set screw and locating mark on outside of the cup.
The guide bushings are aluminum about .003" under groove diameter. They are just driven into the breech end of a new barrel to engrave the lands. They will be tight at first but will loosen up with a bit of use. I use 6-48 scope base screws to hold the bushings on. After broaching the button in the rifling rotate the button so the groove is lined up with the locating dot on the end. I made one for .264" and up and another for 6MM. Then I had to make one for .224" which makes no sense as the gas port is bigger than the groove is wide. But it all pays the bills.
I have to reset my work offset to do the rest of the machine work but this adds less than 5 minutes to the job.

You owe me a beer next time we meet.


start


end point

fixtures and button

 

[LVLAaron]

Thanks so much Dave! Like I think someone else said, sort of like clocking a bolt action barrel. Do the tenon, then adjust it. Now I get to do what I enjoy most, make little jigs and fixtures!

 

[Kurz]

You owe me a beer next time we meet.

Amen brother! Well done!

 

[dellet]

You owe me a beer next time we meet.

I bet if everybody that doubted you pays off at the same time, your ports won’t line up for a month.

 

[SKWERLZ]

Thanks so much Dave! Like I think someone else said, sort of like clocking a bolt action barrel. Do the tenon, then adjust it. Now I get to do what I enjoy most, make little jigs and fixtures!

Lol.

 

[SKWERLZ]

OK here goes.
The process then pics.

Completely machine tenon.
Screw extension on and mark the barrel top dead center using the locating pin. See pic. This is your starting point.
Set indexing fixture for the length from the shoulder to the gas port.
Run indexing fixture in to see where you have to go. Make a second mark. This determines the amount of rotation need for proper indexing.
Back the extension off a bit and face the barrel shoulder off until you have about an 1/8th of an inch left to rotate.
I use a grooving tool to cut all my shoulders, Better finish which adds predictability to the rotation. The other variable is the quality of the extension. All extensions go into the parts washer and get cleaned with a wire brush to remove debris from the threads.
After facing the shoulder and adjusting the rotation set your digital readout to zero or use a 2" travel indicator. Run the carriage back to the tenon length and face to length. That is never more than .010" at most unless you over shoot the mark.
Proceed with chambering and any other work on the end of the tenon.
Next turn gas port area to diameter and the shoulder to the correct location.


You have to do multiple operations when making the fixtures so all indicating surfaces are in alignment.
Example the flat on the rod for the cup has to be indexed with the center drill dot on the front end. Same with the set screw and locating mark on outside of the cup.
The guide bushings are aluminum about .003" under groove diameter. They are just driven into the breech end of a new barrel to engrave the lands. They will be tight at first but will loosen up with a bit of use. I use 6-48 scope base screws to hold the bushings on. After broaching the button in the rifling rotate the button so the groove is lined up with the locating dot on the end. I made one for .264" and up and another for 6MM. Then I had to make one for .224" which makes no sense as the gas port is bigger than the groove is wide. But it all pays the bills.
I have to reset my work offset to do the rest of the machine work but this adds less than 5 minutes to the job.

You owe me a beer next time we meet.


start
View attachment 1762136

end pointView attachment 1762137

fixtures and button

View attachment 1762138View attachment 1762139View attachment 1762140
View attachment 1762141

Your fixtures are a lot cleaner than the clunky setup I made.

 

[ShaunBrady]

Wow

You've completely unwound the knot I tied myself in by target fixating on the port.

By starting with the barrel extension, its installation is reduced to a simple clocking operation of no more than 1/4 turn with a 4 groove barrel. The timing fixture is no more complicated than any of the other dedicated nonsense we make or buy for individual operations on other makes. It can be done on manual machines.

If the best test of an idea's elegance is its simplicity, this is one for the ages.

I can't wait to try it.

Thank you for the gift.

 

[padom]

Just received this Geissele 18" cut rifled SPR barrel today. These shot amazing when first released and have been out of stock for a long time. Just came back in stock the last few weeks.

I have read reports of guys all saying Geissele is centering their gas ports.

Just unboxed mine and sure enough they are centering them.

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