Originally Posted by Mr. Deer Hunter

Check the head space by putting the bullet into the barrel with your finger and push it forwards as far as it will go and then close the bolt and take a measurement and then push the round back with a ram rod and take another measurement from the top of the barrel down to the shell. It takes a depth mic to do it and a precision rod of the correct length and size not to damage the bore.

That is how a real gunsmith checks it.