Best Way Or Tool To Check Headspace?

[MOOSE 4 GOD]

Thanks again Rocky:

So let me ask one more Question. I'm loading a 7mm Rem Mag in a new TC PRO HUNTER. I only neck size or at least that is all I ever done for the last 18 years in a bolt action. My question is as long as I check the OAL of my brass and it goes in and out of my barrel with ease do I even have to worry about the word HEADSPACE?

Thanks
Benny