headspacing

[brian923]

best way to do it for an ar-15? is there a mathmatical equasion that is used? i am wanting to make an ar-15 barrel, and with those barrel's, the extesion is threaded to the barrel itself. can i use a gauge and the bolt to make the final adjustment to the chamber? what i am trying to say is, if i use a go gauge, can i ream the barrel, intall the extention, place the go gauge in the chamber and try to see if the bolt locks. if not, ream a bit more until i have lock up! or is thre an easyier way? ,or do i not even have a clue?) thanks guys, brian.

 

[krxm21]

You have the right idea. Thread the barrel for the extension.
Mark the reamer with layout die or better yet use a reamer stop to insure that you don't go in too far. When you are close: use only light cuts to get the bolt to close on the go gage.
Clean it up, torque the extension down, double check with gages.
Done.

BTW clean the chips from the reamer frequently.
Kent

 

[brian923]

Thank you krxm21. another question. do i need both the go and no-go gauges? or is the go-gauge good enough.,im guessing that the no-go gauge is for measuring older barrel headspacing.)

thanks again, brian.

 

[kaferhaus]

actually, you can use a full length sized case as a "go gage".

The datum on that case will be the same as a no go gage.

Further, you'll know that every time you size a case, it'll be perfect for that chamber.

I and many "big name" smiths chamber rifles that way even though we have the headspace gages on hand. I always ask a customer to send me a couple cases full length sized with their dies.

Now if it's a hunting rifle... I just use the gage.

 

[chris]

There is anpother way...put your bolt in the extension in the locked up position in your vise...take you depth mic and measure down to the bolt face..do it in three or four places. Say that measurement is 0.900" then subtract 0.002 for the "crush fit" when you torque on the extension. Then ream your chamber to your headspace number,0.898") measuring with a go guage in the chamber to the shoulder on your barrel. Not to step on any toes, but I would never use a sized case to set headspace....as the die can be adjusted for a huge difference i sizing- meaning the sized case could be 10 thou too short or too long....that's what they make gauges for and at $20, they are cheap insurance to keep you out of an expensive lawsuit.

 

[brian923]

thank you. but....... just to clearify, do i do this with the extension on or off the barrel. just trying to make sure i am on the same page. thanks again, brian

 

[chris]

extension off

 

[brian923]

oooooooooooooooooooohhhhhhhhhhhhhhhhh!!!!!!!!!!!

okay, i see where your going with this. just clicked, and now we are on the same page. thank you again, brian.