J E Custom
Well-Known Member
1. Head clearance is the air space between the rear of the case and the bolt face. And the head clearance is equal to the amount of shoulder bump. The rifles headspace is the distance from the bolt face to the datum point on the chambers shoulder.
Wrong again. Head space is the air space between the Head space gauge and the bolt face. WE don't set head space with a cartridge If we want it to be precise. Head space will change from one brand of cartridges to the next, because they have a minimum and maximum specification that gives them a range of lengths that they have to manufacture their ammo buy and it is normally in the middle of this range so it will chamber in most all chambers. Some manufactures like Winchester will tend to size their ammo On the small(Short) side and others will size their cartridges near the maximum length like Hornady and if a chamber is cut to minimum length, Some ammo will not chamber. Head space is therefore normally set 1 to 3 thousandths more than the head space gauge. Once they are fired, essentially there is no head space until it is sized. and depending on the sizing philosophy, there may still be no head space. PS: I cant find any head clearance gauges, Only Head space gauges.
2. The OP didn't need to take the rifle to a gunsmith and check the headspace. The OP cases grew in length when full length resized and squeezed making them longer in over all length.
In the beginning he did not know what the problem was and was looking for a way to find out if he had excessive head space that could cause case head separation. Without the proper head space gauges That any gunsmith would have it would be just a guess so he solved the question by sectioning and eliminated the question.
1. The primer is the first thing to move to the rear when the cartridge is fired by the amount of head clearance.
2. P.O. Ackley did a experiment with a 30-30 Winchester rifle and removed the rifles locking bolt. He then remotely fired the rifle and the only thing that happened was the primer moved to the rear. When the cartridge fired the body of the case gripped the chamber walls and the chamber pressure was not great enough to cause the case to stretch to meet the bolt face.
This one still makes me laugh because first, How would you know if the primer moved or not, unless you had a bad load or a concaved bolt face that would allow the primer to protrude enough to feel it or had a primer pocket that was expanded bad enough not to hold the primer in the first and/or it was over pressured enough to let it blow and we all know what this leads to. I have fired thousands of military ammo that the primers were sealed and even sealed lots of primers my self and the seal never broke even though the primer was flattened because it didn't move. So if you are having this problem you have something wrong with your firearm or your loads.
I am a big fan of PO Ackley and read almost everything he wrote and
he did lots of testing on things that would not be normal and he himself said many times that you should not try this test because it could be fatal if not under controlled conditions. He also blew up many different actions to see how strong they were. Also he decided that if you reached enough pressure that the primer would be blown out and so would the cartridge once it reached enough pressure to overcome the case grip on the chamber. and without the bolt to restrain the case and the primer all of it would be blown out. (The reason for the bolt in the first case) and it would result in one shot only by the shooter). Excessive head space is the main reason case head separation occurs with cartridges whether it is built in to the chamber buy poor head spacing or over sizing cases when reloading them. The only other cause is case fatigue
from many firings and over pressuring the case.
J E CUSTOM