Calculating max headspace

[DrJeckyl]

I figure this would give me at least an idea that if I had difficulty chambering a round, then it would not be a headspace issue.....took a few calculations and need some critique to determine if I arrived at this correctly.

I used a digital caliper and measured from the muzzle to a rod inserted in the barrel,coated of course). The case I used I plugged up evenly with the neck so the OAL of the case was my measuring tool.

With the bolt closed, I zeroed the caliper then I chambered the test cartridge and the reading was 2.0305, case length is 2.032. Headspace on test cartridge is 1.628 leaving .404 from datum on shoulder to end of case, equaling 2.032.

So if the case was flush against the bolt face, I should have a reading of 2.032, so with 2.035 there is a difference of .0015..so if I add that to the existing headspace would my max headspace be 1.6295? Providing of course I had no error in any rod flex or my measurements, but for sake of arguement, all was precise.

Generally when I get a stubborn round, my headspace measurements are around 1.6285 so i'm hoping im on the right track...mainly trying to figure out my bump.

 

[kelbro]

Much easier with a Hornady Head and Shoulders gauge.

 

[DrJeckyl]

That's how I measure my headspace of my brass like i said, but won't give me the headspace of the chamber. Granted it's pretty much .001-.0015 greater than the fired brass but how much spring back is never known.

I figure that knowing almost exactly what the fixed headspace is would aid in sizing the brass. The extractor pin or whatever it is, pushes the case against the shoulder but can leave a gap to the boltface so when fired the case will move against the face exposing a larger jump for the bullet.

More than likely a smith will cut the chamber to SAAMI specs but I like to know what the numbers are regardless.

 

[Stonewall]

Buy a simple go headspace gauge . Use this to measure the actual headpace of your rifle and die set up .

This way you have a repeatable base measurement to start from .
The RCBS precision mike style tool would possibly be easier to use.

Glenn

 

[kelbro]

I get what you are saying now. Using the headspace gauge would be a great method for determining the length. You can remove the ejector from the bolt and shim the gauge with layers of scotch tape until you get the fit you are looking for. Then measure the gauge.