Concentricity Tools

[silverhawk]

A colleague of mine had a few concentricity tools, and he sent me one. It was unopened, new-in-box shape. It's a Hornady tool. The frame was aluminum. I started to play around with it, but my machinist brain is immediately questioning the tool. As I see it, it takes the bullet in one spindle, and the case butt in the other. The dial indicator (sits on a Picatinny rail without the slots as a cheap form of a dovetail) looks to be a cheap, re-badged harbor-freight dial indicator.



Based on the dial indicator only registering on the shoulder of the casing, it will have some limitations. For example, the "runout" of the bullet isn't being directly measured, and the "out of round" on the casing will only show part of how far the bullet is out. It seems like it will be misleading, and you can't tell if it's seating concentrically on a different axis that is angled from the casing, or if it's a different but parallel axis. Do most concentricity tools function this way? My brain says a tool for measuring this kind of thing would hold tight on the casing, and then measure the bullet directly.

 

[Tozguy]

I think that you have a good point. If the necks are carefully turned and the bullet seated straight then what would that 'concentricity' tester show? If there was any runout to speak of using that tool I would suspect the resizing die or the chamber being lopsided. I would not consider just prying the round at the neck to straighten it as a solution.
When I check concentricity I just roll the round over a flat surface and look for wobble of the bullet tip. Like we do with pool ques.

 

[silverhawk]

A lot of cartridges have sloped sides. Is it possible to solidly grab a sloped or conical part using an ER collet? Might be worth some simple design changes using commonly available parts if I could.

joe

 

[Flyinfool]

You need 2 points of reference to create a line. The Concentricity tool is using the base of the case and the point of the bullet to define that line. From there you can measure the concentricity at the shoulder, on the neck or the bullet at the case neck. If the bullet is seated off axis this will still show up in the measurements. Holding tight on the casing accurately would be extreemly dificult with all of the different case shapes there are. ANd then there are the acceptable tolerances on those case sizes and shapes, especially when you start to look at wildcats and fire formed cases. No the method used by this tool is not perfect, But it might just be the most repeatable and the best compromise.

 

[wrat]

Per ANSI GD&T, Concentricty is not the same as TIR. This tool, at best, can report Total Indicator Runout.

In handloading, a lot of things can happen to the brass. Dents, deformations, and various twists. Sometimes these warps are not plainly visible to the naked eye.

So, you run your brass through your full length sizing die. Should be great, right? Well, it MIGHT be. But the brass flows and it flows differently than you think it ought to sometimes. There's a lot of variations in the same lot of brass, even with the same guy running the handle at what seems like the same speed, same pressure, and same travel. Despite best efforts, it might not be as perfect as you'd like. So even after sizing, there can be warpage especially in the shoulder.

The idea is to run your lot of brass through your sizing die. Then you have a tool very similar in appearance to this one where you trim the case to length (checking carefully with your calipers). Then this station to check runout. Is it all over the place? Maybe need to run it through sizing again. Why? who knows? who EVER knows? If just does. Maybe you look to see if you need to adjust your process.
Or maybe it's fine. Maybe it's "right on".

Point being, you can load millions of rounds and never once use this thing. It's just another check that can maybe make a difference.

 

[mmcmdl]

Per ANSI GD&T,

Funny you should bring this up . I was looking for something else down the basement for Alloy and found 2 copies of GD&T books I stashed away years ago . I'm going to pass one on to Aukai and get rid of the other one . I'll post it in the book section .

 

[pontiac428]

It your rounds are curved like a banana that gauge would pick it up. It will show if the cartridge is off-axis along its length. I've never felt the need to use one myself, because the only thing I might learn from it is that if I don't like how it looks on the gauge, I would have no choice but to toss out my seating die.

 

[lordbeezer]

I made this years ago. Primitive looking but it works. Use to check 308 brass or bullet run out. Can move around to check .223 but don’t very often.

 

[silverhawk]

I made this years ago. Primitive looking but it works. Use to check 308 brass or bullet run out. Can move around to check .223 but don’t very often. View attachment 342281

That is pretty much what I expected these to look like and function like, and I'd see fewer issues with yours than this professional one. Did you use bearings on the casting holder?

joe

 

[lordbeezer]

No sir. Took couple machined flat washers. Cut triangle out then knife beveled edges. Brazed to adjusting stud. I’m using bonanza benchrest sizing and seating dies.