With only the GO headspace gage, a Precision Mic and a spent fired primer you can get your exact headspace reading.

[img width=337 height=450]http://i122.photobucket.com/albums/o254/bigedp51/IMGP7241.jpg[/img]

To get your head clearance or "air space" between the bolt face and the the rear of the case all you use is a spent fired primer and a new or full length resized cartridge case.

Step one, measure the length of your case and write it down.

[img width=600 height=450]http://i122.photobucket.com/albums/o254/bigedp51/IMGP0710.jpg[/img]

Next just using your fingers insert the fired primer into the primer pocket just starting the primer into the pocket.

[img width=564 height=450]http://i122.photobucket.com/albums/o254/bigedp51/IMGP0704.jpg[/img]

[img width=600 height=450]http://i122.photobucket.com/albums/o254/bigedp51/IMGP0706.jpg[/img]

Now chamber the test cartridge and slowly close the bolt seating the primer, remover the cartridge and measure the case again and write it down. Subtract the first case measurement from the second case measurement and this will be your head clearance.

Add the case measurement in the Precision Mic to your test measurement and you will have your exact headspace measurement. Your GO gage will be "zero", your first Precision Mic case reading will be smaller or minus zero and the case test reading will be actual headspace and a plus reading longer than the GO gage.

Below the amount the primer protrudes is your head clearance or "excess headspace" over the length of the GO gage.

[img width=600 height=272]http://i122.photobucket.com/albums/o254/bigedp51/9-2.jpg[/img]

And temperature will not effect your readings as Scotch tape will.