I'm still trying to figure out what your end goal is. There doesn't have to be an end goal. I sometimes look at things just to figure out how they work, but buying headspace gauges isn't cheap and won't really do anything for you other than confirm that your rifle is properly headspaced. It almost certainly will be properly headspaced, especially if you're not having any issues.
I think I'll take the liberty of suggesting a tool that I've found to be very useful. When you're firing ammo in a particular rifle, you're not really concerned about the actual headspace of the rifle. It's the difference between the rifle's headspace and the cartridges headspace (measured from the base of the case to the center of the shoulder) that matters. The cartridge's headspace has to be smaller or else you'll have trouble with it chambering. If you reload, you ideally want to set things up so that the cartridge headspace is 0.001" to 0.002" less than the rifles actual headspace. For a semiauto, you want this measurement to be a more generous 0.003" to 0.005". The reason you need a greater difference with semiauto cartridges is that you have to allow for debris and the fact that the bolt usually does not have as much camming action. Now if you don't have headspace gauges, how do you measure a rifles headspace and compare it to a cartridges headspace? You start with a case that's been fired in the rifle in question. Then you use the Hornady Lock-N-Load Headspace tool on a set of calipers to measure the headspace of the fired case. The headspace of this case will be right at 0.001" less than you're rifles actual headspace due to brass contraction. The really cool thing about this tool set is that you can use it to measure headspace of virtually all bottle necked rifle cartridges.
https://www.youtube.com/watch?v=P-UrMTyJ1_E
http://www.hornady.com/store/Lock-N-...h-Body-1-Each/
So if you don't reload, how does this tool benefit you? Well, you can compare the difference in your rifles headspace (measured from a fired case) to that of new cartridges. Ideally, you want that same 0.003" to 0.005" difference for your AR10. All else being equal (key phrase), a rifle & cartridge combination that's within this difference will be more accurate than one where there's a greater difference. One thing to remember is that rifle manufacturers often headspace their rifles on the high end of the range so that they can be confident all commercially available ammo will chamber. Ammo manufacturers often headspace their cartridges on the low end of the range so that they can be confident their ammo will chamber in rifles that have headspace of the low end of the range. Combine both of these together and there can be way more of a difference than you'd want. Keep in mind that there's more to accuracy than headspace, bullets and powder come to mind first, so measuring headspace is just one part of the equation.
The bottom line is that I think this tool will be much more useful for you than a set of headspace gauges for probably about the same money.
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