There are 2 . Cartridge headspace is controled when you full length resize a case with your reloading dies. Push the shoulder back to far and you have excess headspace. Chamber headspace is fixed in the rifle,it runs for the bolt face to the chamber area or datum line where the shoulder of the case would make contact. Bottle neck types. Both, if not correct, can cause case separation. This one happens to be in an old militay surplus rifle. These guns can have mismatched bolts, causing excess or tight headspace. Play it safe, have headspace checked by a gunsmith. Excess chamber headspace can be helped by Partial Full Length Resizing, if done correctly.