Reading a sinclair concentricity gauge

[GW Hunter]

Probably going to get one of these, I have one question though. When the dial indicator moves between values, is the runout value half of the total movement?

 

[SealT5]

If I'm reading your question right the value you are seeing is the full value of runout you have

Joe

 

[J E Custom]

If I'm reading your question right the value you are seeing is the full value of runout you have

Joe

You are correct Joe.

When you rotate the case one full revolution. It measures the total run out of the case neck. I like to check the run out of a fired case to check the chamber concentricity and then check the run out of the same round after its loaded. This tells me if I an contributing the the run out with my loading process.

In my opinion, these are invaluable tools if precision loads are desired.

J E CUSTOM

 

[bigedp51]

Probably going to get one of these, I have one question though. When the dial indicator moves between values, is the runout value half of the total movement?

Bullet Concentricity & Related Issues
https://www.sinclairintl.com/guntech/bullet-concentricity-related-issues/detail.htm?lid=16572

 

[bigedp51]

You are correct Joe.

When you rotate the case one full revolution. It measures the total run out of the case neck.

Only if you subtract the variations in neck thickness, meaning if the case neck varies .003 in neck thickness you subtract .003 from the neck runout.

 

[GW Hunter]

OK, I get that. Maybe I'm over thinking it but, without taking into account neck thickness for simplification, If the neck measures .004 out wouldn't it have to move .002 to even out? making the run out .002? Am I looking at it incorrectly? Thanks for your patience...

 

[J E Custom]

Only if you subtract the variations in neck thickness, meaning if the case neck varies .003 in neck thickness you subtract .003 from the neck runout.

Actually, If the neck wall has any difference you will be wasting your time checking for concentricity because ether the inside or the outside will not be concentric. If the outside of the neck is concentric and the wall has any variations in thickness, the bullet will not be concentric to the bore.

Ether condition is not conducive to good accuracy. Start with uniform neck thickness and then and only then run the concentricity test for any benefit.

If a chamber is truly concentric and neck thickness is consistent, there should be NO run out in fired cases.

J E CUSTOM

 

[bigedp51]

Actually if you are checking neck runout after sizing you must subtract the neck thickness variations from the reading. You want to find out how much runout the neck has and if the sizing operation is causing the runout. On a neck turned case you will not have enough neck thickness variations to effect the neck runout reading. So the readings depend if you neck turn or not on your runout gauge.

And after you seat the bullet you check for bullet runout and if seating is causing any neck runout.

I do not check neck runout on fired cases because I full length resize. And checking neck runout after sizing tells you how straight the neck is after sizing.

I have both runout gauges below.

The top image below is how the Hornady gauge holds the cartridge, by the case rim and bullet tip and reads less than half of the bottom gauge. The bottom gauge spins the case on its body and reads over twice as much as the top Hornady gauge.

The problem with the Hornady runout gauge is you can not check neck runout after sizing. Meaning you will not know if the runout is caused when sizing or bullet seating.

 

[bigedp51]

OK, I get that. Maybe I'm over thinking it but, without taking into account neck thickness for simplification, If the neck measures .004 out wouldn't it have to move .002 to even out? making the run out .002? Am I looking at it incorrectly? Thanks for your patience...

As long as the fired case body does not warp and become egg shaped the Sinclair gauge is spinning the case on its center axis. Meaning any runout you see is the total amount of runout.

Below the case neck has been pulled off center by the expander and the bullet is rubbing on one side of the throat.

This is why the Forster full length benchrest dies with their high mounted floating expander produce cases with so little neck runout. The expander enters the case neck while the neck is held and centered in the neck of the die and does not pull the necks off center.

 

[Mikecr]

Straight ammo reads so on a Sinclair/v-block runout gauge.
Doesn't matter about brass thickness variance, and there is no funny math or manipulation to it.
Straight ammo is also concentric, while concentric ammo isn't necessarily straight at all.

With the Sinclair, Just indicate off seated & exposed bullet bearing prior to nose begin. That is, between case mouth and bullet nose.
With my chambers straight enough is 1thou or less TIR. With bigger chambers/more clearance it could be 2-3thou or even more before affecting results.
This all works out fine because the tighter the clearances the straighter ammo is made (from that). With looser clearances, and more sizing, runout grows bigger. But again, it matters less here.

Also, with mandrel pre-seating, and no body sizing, I can make dead straight ammo regardless of thickness variances. This is fine provided enough neck clearance for excess thickness here or there. To run with low neck clearance, I turn necks.
I can also make crooked ammo with cases having zero thickness variances. But I measure every loaded round, to make sure that doesn't happen.

 

[HobieH3]

As long as the fired case body does not warp and become egg shaped the Sinclair gauge is spinning the case on its center axis. Meaning any runout you see is the total amount of runout.

Below the case neck has been pulled off center by the expander and the bullet is rubbing on one side of the throat.

This is why the Forster full length benchrest dies with their high mounted floating expander produce cases with so little neck runout. The expander enters the case neck while the neck is held and centered in the neck of the die and does not pull the necks off center.

Looks incredible. Expensive? SAAMI only, or custom from fired cases?

 

[SealT5]

I'm with @J E Custom Without consistent neck thickness your raking leaves in the wind

 

[bigedp51]

Bullet Concentricity Basics — What You Need to Know
http://bulletin.accurateshooter.com/2019/02/bullet-concentricity-basics-what-you-need-to-know/

 

[ar10ar15man]

big ed loves charts graphs color presentations.
mikecr likes facts
i go with mike every tme