cirles wrote:Hi there,
When measuring for ‘Headspace’ in a firearm, should the ‘datum’ measuring point be taken near the shoulder case end (as opposed to the other shoulder neck end) or approximately half way along the shoulder?
Am totally new to reloading rifle or handgun shooting. Will begin to start reloading for 6.5 Creedmoor cartridges. So the above question regarding using a datum dial comparator device to measure Headspace. The device manufacturer (Forster) indicated that I use the .400 hole for this purpose (which measures the datum area just above/below the shoulder area (angle) of the case end (as opposed to the neck end shoulder). Now when I looked up a Hornady device used for this purpose (youtube – not a rep.) he indicated to find the correct datum hole size to use, 1st measure the neck diameter at the shoulder area & then also the case diameter at the other shoulder area, add these two figures together and then divide by 2 (to get a measure of approximately half way down the shoulder). This final figure is used to determine which hole size to use by choosing the closet one to your arrived figure. When I did this for the 6.5 cartridge, the figure came to exactly .375, thus another datum hole, which when eyeballing the cartridge this measures to the half way area on the shoulder.
Which is the best for use of determining the (relative) measure for headspace (I understand that as long as you remain consistent in what you use that perhaps there is no issue?).
Headspace is a measurement in the firearm, it has nothing to do with your brass.
I'm thinking you are using a comparator to set your shoulder when sizing your brass?
I would simply adjust the die bumping the shoulder slightly until it just chambers fine, then put your comparator on that case and use that as your setting, regardless of the position on the shoulder.