Does virgin brass show false pressure signs?

[Dski48]

I loaded some virgin Lapua brass with 43.5gr of varget and 168gr Berger's. When I took them to the range and shot them some of the brass had the faint extractor circle marks on the rim and others didn't. The velocities were close to each other so it wasn't like the loads varied wildly. It was sorta random on when the marks would show up

 

[XLR308]

Could be that the headspace on the new brass is at the upper end of the tolerance to your chamber.
What does the brass base to datum measure after firing compared to the new brass ?

 

[Dski48]

Bear with me I'm sorta new to this long range stuff. What's the datum line?

 

[XLR308]

It's a measurement from the base to a point on the shoulder.
You would also use it for measuring shoulder bump on your fired brass for proper sizing to your chamber.
If the headspace on the new brass is on the large side when you chamber and fire a round the brass is slamming back into the bolt face during expansion and causing you to see occasional ejector marks on the case heads.

 

[Dski48]

So I full length sized all the brass prior to loading for the first time wouldn't this make all the cases be the same dimensions?

 

[XLR308]

Your making the assumption that all were identical to begin with and without actual measurements after sizing again assuming you were bumping the shoulder at all.

If a full length die isn't adjusted down far enough to contact the shoulder the base to shoulder measurement can actualy grow.
That's mostly with fired brass but without actual measurements again it would be assumption.
Another issue is excessive neck tension on new brass and dragging the button back through the necks causing inconsistencies.
Eliminating the button on your die and running a turning mandrel through the necks will greatly improve inconsistencies with neck tension.

 

[Dski48]

I guess I need to buy the Hornady tool thing that measures my shoulders. I've been on the fence about getting one. I have the comparator for doing the ogive I just need a different insert for the shoulder right?

 

[Cascade Hemi]

Bear with me I'm sorta new to this long range stuff. What's the datum line?

He's asking if you measured your brass and how much it grew. Hornady sells comparators for measuring distance from the case shoulder to base. They are inexpensive and invaluable for setting up your sizing dies as well as diagnostic measurements.

 

[Dski48]

He's asking if you measured your brass and how much it grew. Hornady sells comparators for measuring distance from the case shoulder to base. They are inexpensive and invaluable for setting up your sizing dies as well as diagnostic measurements.

No I didn't. I don't have the comparator for measuring the shoulder. Just the one for doing ogives

 

[918v]

How to the lands were you?

 

[Cascade Hemi]

No I didn't. I don't have the comparator for measuring the shoulder. Just the one for doing ogives

To answer your original questions, new brass is smaller than fired brass so you may have a little more pressure. Did you measure your distance to lands? If you did, how far off the lands did you load the cartridges? If you're a new hand loader, consider buying the Hornady head space comparitor and OAL gage (with specific case).

 

[Dski48]

To answer your original questions, new brass is smaller than fired brass so you may have a little more pressure. Did you measure your distance to lands? If you did, how far off the lands did you load the cartridges? If you're a new hand loader, consider buying the Hornady head space comparitor and OAL gage (with specific case).

I was 20 thou to the lands

 

[Cascade Hemi]

I was 20 thou to the lands

Without knowing anything about your rifle or seeing your ammo the short answer is you are showing pressure signs. You should start 10% below book data because of the brass. What is your velocity?

 

[Dski48]

I'm at 2650 fps. My rifle is a savage 12fv 308.

 

[918v]

Back away from the lands

 

[spife7980]

If you sized it too much you could have given it space to move around in the chamber and that could be enough space for the brass to slam back into the bolt face in combination with the smaller volume and you got some not false signs that might not be there with formed brass.

Pick up a hornady headspace headspace bushings and a hornady bullet comparator that can attach to your calipers. That will enable you to measure your brass shoulders via datum. A datum is a plane. As we use it, it’s the point where a plane cutting intersects the shoulder at a certain diameter.

 

[Dski48]

If you sized it too much you could have given it space to move around in the chamber and that could be enough space for the brass to slam back into the bolt face in combination with the smaller volume and you got some not false signs that might not be there with formed brass.

Pick up a hornady headspace headspace bushings and a hornady bullet comparator that can attach to your calipers. That will enable you to measure your brass shoulders via datum. A datum is a plane. As we use it, it’s the point where a plane cutting intersects the shoulder at a certain diameter.

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I just ordered a .400 bushing. Hopefully I just have my dies set up wrong and I'm not over pressure at that load