Getting accurate brass thickness on cases.

[King_beardsly]

What's the best way to get a pretty accurate brass thickness measurement, I'm currently using a set of digital calipers and consistent pressure isn't exactly easy. I just need to figure out what bushing to order for a forster bushing bump die I'm setting up for 6creedmoor.

 

[One1Bravo]

I use this.

 

[Bradu]

If you already have the dies, seat a bullet and measure the neck then subtract .002".

 

[King_beardsly]

I've got some stuff that loaded up, so I'll just measure that stuff

 

[spife7980]

A micrometer will be more accurate than any calipers. Calipers have a .001 resolution and the good digital ones are a .0005 resolution (x.000-x.0004 would display as x.0000 and x.0005-x.0009 would read x.0005).

Micrometers go to .0001 resolution. You don’t realize how crude calipers are until you use a micrometer. I only have a rcbs ball vernier when it was on sale for dirt cheap just to see for myself but even being a “lower level” tool it reads way in between what my mitutoyo calipers will show.


Unless you are going to consider differing neck tension (funny how this topic has popped up in what I’ve read today) to time your load in addition to powder charge and seating depth then just use your calipers and pick one. Which one depends on if you are going to use an expansion step or not. If no expander then I would choose a bushing .002 smaller than a loaded round. If you will expand then a bushing .004 smaller.

 

[Sheldon N]

Like posted above measure the neck OD of a loaded round then subtract .002 to get your desired bushing size. No need for a micrometer on this step, a simple set of calipers will do.

One thing I'd add is to make sure to measure the neck OD of the brass after it comes out of the sizing die. You might find it smaller or larger than the printed measurement on the bushing and may need to adjust bushing size accordingly. Goal is for the sized brass to be 0.002 smaller than loaded brass.

 

[King_beardsly]

I measured the stuff I've got loaded up and it seems a little on the lower end of what bushing are usually used, I think I'm just applying to much pressure and the calipers are reading to small

 

[White_Shark]

This is what we use for measuring wall thickness at the mouth at Jagemann, very consistent and repeatable.

We rounded off the face to give a smaller contact point for better consistency, but this would work well for home uses as is.

 

[ShtrRdy]

I measured the stuff I've got loaded up and it seems a little on the lower end of what bushing are usually used, I think I'm just applying to much pressure and the calipers are reading to small

I think you would have to push hard to compress brass. Try lightly pressing the caliper jaws around the outside neck.

 

[King_beardsly]

I think you would have to push hard to compress brass. Try lightly pressing the caliper jaws around the outside neck.

I don't think I'm compressing the brass, I think the digital calipers are reading smaller then the actual thickness due to much pressure causing something to shift allowing a false readout or they aren't the best calipers.

 

[Sheldon N]

I don't think I'm compressing the brass, I think the digital calipers are reading smaller then the actual thickness due to much pressure causing something to shift allowing a false readout or they aren't the best calipers.

Doesn't really matter too much what the absolute number is, other than to give some guidance as to what bushing to start out with. The measurement that matters is the comparative measurement between sized brass and loaded round OD. Measure them both in the same place on the neck with the same amount of force and you should be fine.

 

[King_beardsly]

True, I ended up getting a few bushings just below and right at the measurement