6BR Question

[Rogerthatout]

I’m little perplexed with bump and shoulder measurements on this caliber. I’m finally getting though all my virgin Lapua brass so I’m starting to resize.

At datum point .350, I’m get measurements of virgin Lapua brass at 1.162 and once fired
brass is between 1.1635-1.1665 however my spec sheets shows measurement should be between 1.167-1.177…. Wondering why virgin Lapua brass is measuring so far below spec ???

What am I doing wrong or is my diagram wrong?
Can you guys share thoughts on this?

 

[Rocketmandb]

Most brass is on the lower end of (or lower than) spec. Think about it, if you're a brass manufacturer, do you want to get called out because it won't fit in someone's chamber that is cut a little small?

Regardless, don't worry about what virgin brass measures. What matters is that you measure your fired brass appropriately and bump back .001 - .002 when sizing.

 

[Rogerthatout]

Is it possibly my brass is not reaching total headspace on first firing?

 

[Rocketmandb]

Is it possibly my brass is not reaching total headspace on first firing?

Yes - this is why custom die manufacturers want to go off of brass that has been fired at least twice. Still, I wouldn't worry about this at all because your low measurement of once fired comes down to one (or a combination of) three things:

1) your chamber is slightly small.
2) once-fired has more spring back
3) your measuring tool isn't measuring at exactly the right place

Do any of these matter much?

No. Sizing is all relative to your chamber, not a drawing.

 

[Supersubes]

The comparator on your caliper isn't perfect, even the slightest bit of chamfer on its bore will create a short measurement. Or maybe the bore is .352.

Its a comparator, not a gauge. The virgin to fired comparative measurement is right where one would expect it to be.

 

[Rogerthatout]

Most brass is on the lower end of (or lower than) spec. Think about it, if you're a brass manufacturer, do you want to get called out because it won't fit in someone's chamber that is cut a little small?

Regardless, don't worry about what virgin brass measures. What matters is that you measure your fired brass appropriately and bump back .001 - .002 when sizing.

I just took my firing pin out to get good feel of headspace and measurements, my headspace is 1.167… will be resizing to 1.165.

I have two rifles, done by two gun smiths so I’ll need to either bump twice as much as needed to satisfy both rifles or load separately. To complicate things, I have a third 6 BR rifle coming next week. All for my kids…thanks op

At the end of the movie, hoping we can all share DOPE on matches, my original plan was to shoot one Forgiving load so all three of us can focus on dope and fundamentals… even sharing ammo and mags. It’s still possible, it’s still very possible. I’ll measure rifle # 2 soon and rifle # 3 soon and maybe all 3 will be under a MOA w same loads.

 

[jetjock07]

Probably imperfections with the comparator.

 

[Rocketmandb]

I just took my firing pin out to get good feel of headspace and measurements, my headspace is 1.167… will be resizing to 1.165.

I have two rifles, done by two gun smiths so I’ll need to either bump twice as much as needed to satisfy both rifles or load separately. To complicate things, I have a third 6 BR rifle coming next week. All for my kids…thanks op

At the end of the movie, hoping we can all share DOPE on matches, my original plan was to shoot one Forgiving load so all three of us can focus on dope and fundamentals… even sharing ammo and mags. It’s still possible, it’s still very possible. I’ll measure rifle # 2 soon and rifle # 3 soon and maybe all 3 will be under a MOA w same loads.

Different smiths, different reamers, different chambers - keep the brass separate to avoid any issues with stiff/stuck cases.