JeepHammer
Moderator
LE Wilson 'Headspace' gauge IS a Datum Line index gauge, meaning the 'Stop' or index is the Datum Line on the shoulder of the case.
Confusion comes with terminology,
'Headspace' PROPER is from a closed bolt face to the Datum Line contact point in the CHAMBER of the rifle.
The CASE simply fits that rifle headspace or it doesn't...
You are gauging the CASE from head to Datum Line to see if it fits in YOUR HEADSPACE in the rifle.
The case doesn't have a 'Headspace', so 'Headspace' gauge is a bit of a misnomer, but it's common usage since everyone calls them 'Headspace' gauges.
Drop a loaded FACTORY round in the gauge (or several & take the average),
Measure from head of brass to the bottom of the gauge,
This will be your 'Start' or 'Zero' point reading,
YOUR SIZED BRASS will be + or - that 'Zero' point.
Once you produce brass that fits in the FIREARM chamber without feeding or bolt closing issues, that will be your new 'Zero' to work from.
Bump the shoulder back a little at a time until the brass fits the chamber correctly and that is your 'Zero' if you aren't looking to produce SAAMI specification rounds from your brass.
If you are shooting the rounds in more than ONE single firearm,
You have no choice, the brass MUST be SAAMI specification and fit in between the 'Go/NoGo' groove on the head end of the LE Wilson gauge.
Don't attempt anything tricky until you gain experience!
It's either/or...
Either you produce SAAMI specification tolerance brass,
OR, you produce brass for one single firearm...
Right now, you simply don't have enough experience to determine which firearm has the tightest chamber and produce rounds for multipul firearms that are not SAAMI spec.
That case gauge has a groove cut into both ends,
Head end is minimum/maximum for SAAMI chambers,
Mouth end is minimum/maximum trim to lengths.
The gauge also works as a 'Last Word' gauge for loaded rounds.
It will tell you quickly if you buckled shoulders or bowed cases when loading.
This is particularly handy when making Semi-auto rounds where SHOULDER buckles often happen due to crimping. Drop the reloaded round in the gauge and if it doesn't seat (sticks up) the shoulder is probably buckled and it won't headspace correctly/get jammed in the chamber.
(Virtually every new loader buckles the shoulder at one time or another)
Confusion comes with terminology,
'Headspace' PROPER is from a closed bolt face to the Datum Line contact point in the CHAMBER of the rifle.
The CASE simply fits that rifle headspace or it doesn't...
You are gauging the CASE from head to Datum Line to see if it fits in YOUR HEADSPACE in the rifle.
The case doesn't have a 'Headspace', so 'Headspace' gauge is a bit of a misnomer, but it's common usage since everyone calls them 'Headspace' gauges.
Drop a loaded FACTORY round in the gauge (or several & take the average),
Measure from head of brass to the bottom of the gauge,
This will be your 'Start' or 'Zero' point reading,
YOUR SIZED BRASS will be + or - that 'Zero' point.
Once you produce brass that fits in the FIREARM chamber without feeding or bolt closing issues, that will be your new 'Zero' to work from.
Bump the shoulder back a little at a time until the brass fits the chamber correctly and that is your 'Zero' if you aren't looking to produce SAAMI specification rounds from your brass.
If you are shooting the rounds in more than ONE single firearm,
You have no choice, the brass MUST be SAAMI specification and fit in between the 'Go/NoGo' groove on the head end of the LE Wilson gauge.
Don't attempt anything tricky until you gain experience!
It's either/or...
Either you produce SAAMI specification tolerance brass,
OR, you produce brass for one single firearm...
Right now, you simply don't have enough experience to determine which firearm has the tightest chamber and produce rounds for multipul firearms that are not SAAMI spec.
That case gauge has a groove cut into both ends,
Head end is minimum/maximum for SAAMI chambers,
Mouth end is minimum/maximum trim to lengths.
The gauge also works as a 'Last Word' gauge for loaded rounds.
It will tell you quickly if you buckled shoulders or bowed cases when loading.
This is particularly handy when making Semi-auto rounds where SHOULDER buckles often happen due to crimping. Drop the reloaded round in the gauge and if it doesn't seat (sticks up) the shoulder is probably buckled and it won't headspace correctly/get jammed in the chamber.
(Virtually every new loader buckles the shoulder at one time or another)