Brass Expansion

I purchased a Seekins Havak PH2-NRL in 6 Creedmoor and recently finished firing my first 100 rounds through virgin Petersen brass. Sizing the 1x fired brass was difficult, so I took some measurements of the sized vs fired brass.

The outside neck diameter of the sized brass is .266. The outside diameter of the fired brass is .278, for a .012 difference.

The diameter of the brass body just before the shoulder is .462 on sized brass and .467 on fired brass for a .005 difference.

The FL die is from Short Action Customs and was used to neck size the virgin brass prior to initial firing. All measurements I've taken of the sized brass appear to be in spec with where they should be.

I am trying to determine if the chambering may be too large in the action. I suppose I could measure some sized vs fired brass in other cartridges to compare the variances, but I was curious if anyone knew what the bore chamber specifications should be compared to the brass. Hopefully this question makes sense!

Take a look at the SAAMI spec. I took a screenshot of the drawing I have on the tablet.

Looks like your die is sizing the neck too small.

Is that a small base die? Strange it would size the neck that small though. Are you using the expander that came with the die or a separate mandrel expander?

Bushing with mandrel. ID after sizing is .240 giving me .003 neck tension. So, brass thickness is about .013 on the neck.
.240+.013+.013 would give me the .266.

Fired brass will not go into the head space comparator. It is too expanded in the shoulder area. I haven't seen that before either.

When I compared the two fired case numbers to the drawing for the chamber it looks like the chamber is too large diameter.

ShtrRdy said:

When I compared the two fired case numbers to the drawing for the chamber it looks like the chamber is too large diameter.

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How so? Cartridge neck diameter is only .002 over SAAMI spec when fired which seems tight to me.

Mike D Texas said:

How so? Cartridge neck diameter is only .002 over SAAMI spec when fired which seems tight to me.

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The neck diameter on fired brass is 0.278". The brass would have had some spring back from say 0.279". The maximum neck diameter on the chamber spec is 0.277"

The diameter of the brass body by the shoulder on fired brass was 0.467". The drawing of the chamber spec shows a maximum of 0.463".

I appreciate the input guys. All my other cartridges took more than one during to form to the chamber. This was one firing. Fired brass will not chamber or fit into the head space comparator, and was a workout to resize despite liberal lubrication. Almost took both hands to cycle the press. I doubt this brass will last much longer than a couple/ few firings.

Have you had anything similar occur?

Mickp7 said:

I appreciate the input guys. All my other cartridges took more than one during to form to the chamber. This was one firing. Fired brass will not chamber or fit into the head space comparator, and was a workout to resize despite liberal lubrication. Almost took both hands to cycle the press. I doubt this brass will last much longer than a couple/ few firings.

Have you had anything similar occur?

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I have not had something like this occur. I think I would first contact Seekins and describe what your experiencing and the measurements you've taken.

ShtrRdy said:

I have not had something like this occur. I think I would first contact Seekins and describe what your experiencing and the measurements you've taken.

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I do have a note into them as well. Thanks!

I'm confused how the case won't fit in the comparator.

Philward said:

I'm confused how the case won't fit in the comparator.

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It hangs up about .040 from the case body. It'll go in so far, but expansion at the body/ shoulder junction stops it. Therefore there is no way to measure shoulder bump short of resizing long and working back.

Philward said:

I'm confused how the case won't fit in the comparator.

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If it's Hornady or similar it might be the wrong comparator in use. No where near datum diameter.