“OK guys, then I have a question concerning headspace. I am reloading for a .50BMG and recently purchased a Lyman headspace gauge. Some of my cases are spot on between the minimum”
You have purchased a case gage, back to that part where reloaders refer to a comparator as a head space gage. In the bottom of the case gage is a datum, a datum is not something most reloaders have learned to appreciate. I do not know which 50 BMG you have, I do not know if it is a single shot or if it loads from a magazine. I load for the chamber, I know the length of the chamber from the bolt face to the shoulder of the chamber first.
On the outside chance you do have a head space gage you could use the head space gage to check the accuracy of your case gage BUT! you would still be without a clue if you do not have the means to measure the length of the chamber from the bolt face to the shoulder of the chamber. There are 50 BMBs that are built that are all forgiving when firing for the first time, after firing the first time in chambers that are forgiving when the case is formed I apply the leaver policy, once the shoulder is out there, I “leaver” out there.
Again, we all know the head space gage will allow the bolt to close.