Concentricity Gauge

[PJV99]

So after 15 years of 'conventional' reloading I decided to try and step it up a level.

One thing I have invested in is a s/h RCBS case gauge centre.

So looking at the cartridge 'V' supports they look identical in terms of their profile.

Studying the dimensions of a .308 cartridge the diameter just prior to the neck is slightly smaller than the diameter at the primer end.

So when checking cartridge and bullet runout am I measuring the ruout of an oval rather than a circle?

 

[Bmghunter]

So after 15 years of 'conventional' reloading I decided to try and step it up a level.

One thing I have invested in is a s/h RCBS case gauge centre.

So looking at the cartridge 'V' supports they look identical in terms of their profile.

Studying the dimensions of a .308 cartridge the diameter just prior to the neck is slightly smaller than the diameter at the primer end.

So when checking cartridge and bullet runout am I measuring the ruout of an oval rather than a circle?

No. It's spinning in a circle facing slightly tilted downwards but you are measuring a circle.

 

[PJV99]

I was thinking for it to be a circle doesn't the dial have to be perpendicular to the neck which if the cartridge slopes, albeit only slightly, it isn't?

 

[Dolomite]

As long as it’s spinning in a circle on a level surfaces tilted forward or back it should be concentric. If the surface is warped or bowed it will show up on your gauge.

 

[PJV99]

I was thinking for it to be a circle doesn't the dial have to be perpendicular to the neck which if the cartridge slopes, albeit only slightly, it isnt

 

[Dolomite]

Depending on what type of gauge some are perpendicular and some can be off to the side like the accuracy one or the 21st century gauge. Main thing is the surface that the brass is rotating on is somewhat level whether it be a V block or bearings. Assuming it’s level then the brass is not concentric either from the chamber or the die or die setup.

 

[Rio Precision Gunworks]

It might be easier to visualize this as a tapered cylinder or a cone. Since all a tapered case is, is just a cone that hasn't reached its apex/vertex.

Since you're just touching a single point and rotating the cone, no matter where you put the indicator, you would be measuring the green circle in the pic below. If you kept moving that single point down the cone, that green circle would just become larger.

Say you had that cone in your hand in real life.......would changing the angle or orientation somehow change the dimensions of said cone? Obviously not.

It's no different than your brass case. You can turn it 1000 different ways in your hands or on a table, or in a V block like the concentricity gauge and it obviously stays the same size. So it would also measure the same size at a single point like you are indicating in the gauge.

 

[Aftermath]

It might be easier to visualize this as a tapered cylinder or a cone. Since all a tapered case is, is just a cone that hasn't reached its apex/vertex.

Since you're just touching a single point and rotating the cone, no matter where you put the indicator, you would be measuring the green circle in the pic below. If you kept moving that single point down the cone, that green circle would just become larger.

Say you had that cone in your hand in real life.......would changing the angle or orientation somehow change the dimensions of said cone? Obviously not.

It's no different than your brass case. You can turn it 1000 different ways in your hands or on a table, or in a V block like the concentricity gauge and it obviously stays the same size. So it would also measure the same size at a single point like you are indicating in the gauge.

View attachment 8410872

This...
That vertical axis is what is important to the discussion. If your cone is being rotated about EDIT: an that axis that but the cone center line axis is at an angle, you will see what you are calling ovality. Similarly, if the cone is the projectile that is seated in the case, and if the axis of rotation of the case is not the same axis as the projectile center, you will see a huge plus and minus on your indicator.

I think you'd have to intentionally introduce either condition using modern components.

 

[MarkyMark007]

So after 15 years of 'conventional' reloading I decided to try and step it up a level.

One thing I have invested in is a s/h RCBS case gauge centre.

So looking at the cartridge 'V' supports they look identical in terms of their profile.

Studying the dimensions of a .308 cartridge the diameter just prior to the neck is slightly smaller than the diameter at the primer end.

So when checking cartridge and bullet runout am I measuring the ruout of an oval rather than a circle?

so after 15y of reloading you bought the most useless thing you can imagine...