Measuring neck thickness

[archerforkids]

So... as I jump down this rabbit hole of turning necks, a question arises. Is it important to actually know the neck thickness of our brass, or know what the variance is we see when measuring different points around the neck? What brings this thought to mind, can we establish variation with conventional micrometer or does it have to be a ball micrometer? My knee jerk reaction is as long as we can establish variation, we can obtain out goal. Obviously the accuracy obtained with a regular micrometer is at play here, but is it any easier or more difficult than with a ball micrometer?
Any help is appreciated.

 

[6bra1k]

measure the base of the bullet,seat the bullet about 1/2 down the neck, and then mic in several locations(12, 3,6,9ockock) with a 4 place mic. rotate the round in the mic...is it a smooth rotation...loose contact any where ?

 

[RegionRat]

There is nothing wrong with taking the dimension over a seated bullet. (In some ways, it is what matters more.)
With the ball mic, you can work before seating the bullet and pick up on roughness and noise but the dimension over the bullet is the bottom line in terms of your chamber clearance. YMMV

 

[dannyjbiggs]

My answer to your question is NO. Case neck thickness is NOT a particular concern of mine; but, bullet-loaded-case neck diameter is. My style is to seat the particular bullet that I intend to use in the un-turned case neck of the cases that I will use, and measure that neck loaded diameter. Thereafter, I neck-turn the cases down until I arrive at my desired diameter for the particular barrel chamber neck I will be using.

 

[6BRA]

Just keep in mind...just like the outside of the neck has high and low spots.

the inside isnt much different...

 

[BoydAllen]

You don't really have to have a neck mic......but who would want to seat a bullet every time he wanted to check a neck?

 

[rwj]

You can infer neck thickness by measuring the change in OD. But a ball micrometer is required to directly and accurately measure neck wall thickness. If you’re going to invest in neck turning equipment, a ball micrometer should be included on the essential list.

 

[Straightshooter1]

So... as I jump down this rabbit hole of turning necks, a question arises. Is it important to actually know the neck thickness of our brass, or know what the variance is we see when measuring different points around the neck? What brings this thought to mind, can we establish variation with conventional micrometer or does it have to be a ball micrometer? My knee jerk reaction is as long as we can establish variation, we can obtain out goal. Obviously the accuracy obtained with a regular micrometer is at play here, but is it any easier or more difficult than with a ball micrometer?
Any help is appreciated.

A ball micrometer is best and will work the best and why it's usually recommended for accurate reading on particular areas of the neck. It helps one better see how well the turning processes has done. Only you can decide whether you want that kind of accuracy.

 

[BoydAllen]

Back in the day, 25 or more years ago, I started neck turning with the cheapest neck turner that Sinclair sold. The steel mandrel was crap, both as to finish and material. Because of that, no matter how careful I was the madrel had a strong tendency to pick up some brass directly opposite of where the cutter was applying the most pressure, and although it would be some time before I got my first carbide turning mandrel, getting a neck mic, allowed me to check every neck right after it was turned, so that I could catch a problem right away instead of having a number of necks that were thinner because of the buildup on the mandrel. The area that would collect the brass (on the mandrel) was very small making it easy to overlook. Even after I had better tools I kept the habit of checking my necks after turning which had the additional benefit of my becoming very proficient with the micrometer.

 

[6bra1k]

me...because i shoo

You don't really have to have a neck mic......but who would want to seat a bullet every time he wanted to check a neck?

me...because i shoot loaded rounds in actual chambers, not numbers on paper. it is how i check as i set up neck turners..every time
i have lots of mic's but only loaded dia matters
i agree with boyd most of the time..not this time

 

[6bra1k]

ball mics give SPOT thickness and you are loading a cylinder with a high ring at the base( a bullet with a pressure ring). again it is actual dia vs actual chamber id that counts to give clearance

 

[archerforkids]

Given my goal of most consistent neck tension possible, its fascinating to see all the responses here. I really appreciate the responses folks.

 

[jackieschmidt]

A ball micrometer, and knowing how to use it, is the best way to measure the neck wall thickness.

 

[gunsandgunsmithing]

In a perfect world and in a trained hand, there should be no difference. But in the real world, it's basic tolerance stacking, measuring thickness then doubling that and adding that to another measurement, that of the bullet. I'm in the camp of measuring the loaded round. It's the easiest way and the one with fewest variables, as well as being the one that matters. This is probably the most critical measurement we take as handloaders of the best ammo we can produce.

 

[BoydAllen]

me...because i shoo

me...because i shoot loaded rounds in actual chambers, not numbers on paper. it is how i check as i set up neck turners..every time
i have lots of mic's but only loaded dia matters
i agree with boyd most of the time..not this time

I have checked what I get both ways so I have confidence in what my loaded round clearance will be, having gotten pretty good with my micrometers, from lots of practice. Also my preferred clearance for my 6mm rounds is .003.

 

[Uncle Ed]

 

[6BRA]

the picture on the right is common...even with the best of brass...wouldnt a pressure ring form at the weakest point first? The thin side...sure seems to me it would. I will stay with my ball mics...multiplying by 2 and adding the bullet diameter isnt that difficult.

 

[JFrank]

That picture is a bit of a stretch compared to a real case.

 

[6MMsteve]

I measured 10 pcs of peterson brass at 10 points bout .100 down from the mouth moved down .075 and done 10 more points, it took me awhile I finally fixed a jig out of a shellholder and something else, but anyway I got .0141 to .0143 out of the 20 points, I have never turned any of the Petersooon brass I thought it was good enough for me, ol shaky I can't unshake .0002. now good steady shooters can maybe or can outshoot .0002 not me too shaky and a jerk sometimes

 

[mikecr]

I cull brass by thickness and thickness variance, even though I will likely be turning what I keep.
I do this because brass thickness as seen at necks runs all the way down to webs (at a given taper rate).

If my neck is thicker overall, the case brass is thicker overall.
If there is thickness variance in a neck, there is thickness variance all the way to web.

If the case brass is thicker, it will absorb peak pressure on expansion, differently than the rest.
If the case thickness varies, the case will go banana (high TIR) with sizing cycles.

I want necks showing same thickness overall, with low thickness variance around the neck.
These I'll turn (or not) to desired thickness/clearance for my chamber. The rest I rake into a trash can or sell off. I have picked 50 diamonds from 500 cases, and sold off ~440 (with 10 kept for testing).

The only viable way to do this measuring is with a neck mic having an adjustable ball anvil, and an adjustable mouth stop. As with the rest of the case length, necks taper in thickness, so you need a set datum in measure.