Measuring headspace

[DrJeckyl]

I have the Hornady OAL gauge and now a headspace gauge, have a question regarding headspace between a fired case and the factory case supplied with the kit.

Headspace on the Hornady case supplied with my OAL gauge is 1.625, a fired case is 1.628. When I take a reading with the OAL gauge and a 123 scenar I get 2.281 from base to ogive when touching the lands.
To set a jump of .020 should I add .003 to the length to compensate for the longer cartridge since the neck of the fired case is actually .003 closer to the lands?

I know it's not much difference but am I computing this correctly?

 

[britz]

sounds right.

 

[Calumet]

DrJeckyl

If you think about it, the OAL guage is only measuring the distance from the case shoulder to the lands. I feel this is not a true measurement from the bolt face to the lands.
A true measurement could be obtained by threading a case for the Hornady tool that was fireformed in your chamber. then measuring.

Calumet

 

[DrJeckyl]

I understand what you are saying, I should have added more info.

When I first measured the distance to the lands, I used the OAL gauge and the supplied case, measuring from the rear of the case to the ogive of the bullet...granted the distance should be the same on the Hornady case and my fired case but the distance the ogive is from the lands won't be the same because the neck is extended further into the chamber.

So what i'm getting at is if I loaded the Hornady case,just for sake of argument) to a set distance and a fired case to the same length, the fired case would have the bullet closer to the lands since the shoulder is what keeps the cartridge from going any further into the barrel, and the fired case is .003 longer in headspace.

If this is correct, then the non-fired case would have movement in the chamber fore and aft much more than a fired case.

Right?


Yes I do need to get a fired case threaded for the OAL gauge.