Ar-10 Barrel Extension Threads?

[Msalm]

Measure your extension with the bolt locked in just like you would a bolt gun. Headspace and tenon length can both be taken off those measurements. Only have to add the chamfer/cone for feeding.

 

[jandmtv11]

This post and the barrel extension drawings were extremely helpful.

 

[jandmtv11]

Deleted.

 

[jandmtv11]

Yes, 1" -16. Here's a pic I have hanging around.
View attachment 126990

Is that a drawing of a dpms extension or a armalite extension?

 

[dave2176]

Sorry for bringing up an "older" thread but I have a few questions. I am about to rebarrel my AR308 in DPMS bolt pattern and this is the only drawing I could find online that remotely gave any dimensions.

The shoulder that has the diameter of .920"....is that shoulder always needed and does it need to always be .22"?

The drawing also shows that the case needs to stick out of the chamber .145"....does that always need to be that measurement?
On a bolt rifle, one would measure the distance from the edge of the receiver/recoil lug down to the bolt face and then add a clearance amount. I just dont know what the clearance should be on a gas gun from the front of the bolt lugs to the barrel.

I have rechambered many bolt rifles and so I know what kind of clearances are needed for those but chambering an AR308 is new to me.

I don't think you need the shoulder. I did mine without it because I didn't know about it. The problem is you run into thread issues because the extension thread is not quite complete. You need to file a bit of the thread at a minimum because it gets to tight. As for the .145 sticking out of the chamber, I simply measured the pocket in the bolt where the cartridge sits. I allowed a couple thousandths for the bolt to rotate without binding. Turned out great (I think). You can see it here: http://www.hobby-machinist.com/threads/my-ar10-build.45654/

Is that a drawing of a dpms extension or a armalite extension?

It is DPMS. Check the chart in the thread just above that list differences.
Dave