Headspace

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Srt4ever
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Posts: 19
Joined: Sat Nov 07, 2020 2:33 pm

Re: Headspace

Post by Srt4ever »

Here are some pictures I took. I zeroed my indicator on the max headspace. So when I put it on the minimum it will read -0.005, then the fire formed case is measured next and it measured -0.006 or -0.007.

The brass I sized measures the the same if not it goes down to about -0.008.

Shouldn’t a fire form brass measure positive so that I have to bump the shoulder back a bit ? Isn’t -0.007 to -0.008 to much shoulder bump ?

https://ibb.co/NgRnB8t
https://ibb.co/Qpbj0Hv
https://ibb.co/zRtzXb7
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dellet
Silent But Deadly
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Joined: Fri Nov 30, 2012 1:25 pm

Re: Headspace

Post by dellet »

Still trying to figure out what Gage you have.

If it will accept a fired round, it is probably the headspace gage. That is not a given with subs.

If it is a headspace gauge, it should have 3 levels. Maximum/0, -.005” and minimum -.010”. Some of the Wilson gages measure minimum/-.010” on one end and .005” on the other. Some it is 2 steps on one end.

You have a misunderstanding of the gage, headspace or both.

If the top of the gage is “0” headspace/maximum length and the case is .007” below that, it indicates that your chamber is .003” shorter than maximum length.

If you look at the SAAMI chamber drawing you will see headspace defined as 1.0789” min, 1.0889” max. A .010” window. In theory your chamber will be 1.0859”.

I say in theory because your brass is not full fire formed, and there absolutely no reason to bump it at all.

If you set your die as most manufactures recommend. Contacting the shell holder plus a half turn or what ever, you will be sizing your brass to minimum spec. If you want your brass to grow, so you can set it back based on maximum chamber length, you will need to back the die off so it does not touch the shoulder.

Most likely if you do that, what you will find is that the sized case will get longer and fit higher in the gage than the fired case. If you squeeze the sides of the case to a smaller diameter, the case length will grow in length. As long as the shoulder is not stopped by contacting the die.

As long as a case sized that way chambers, fire it again and repeat until it will no longer chamber, or is longer than the minimum headspace length on the gage.

Just to touch on the confusing part, in case this is what you are hung up on. Cartridge cases do not have anything to do with headspace. They are sized to fit available chamber space between the bolt head and whatever stops the case from going forward. The shoulder on a bottle neck case, rim on a rimmed case, neck on most pistol cases.

So minimum case length, the shortest, creates maximum headspace. The area from bolt face to chamber wall. Minimum headspace is created with maximum cartridge length measured from the bottom of the case to contact point in the chamber, the datum line defined in the specs.

Your round that is .007” below the minimum line, creates near maximum headspace. If you had a way to measure your case you would have an actual number to work with. Not knowing the exact depth of your gage there is a certain amount of guessing.

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