Sinclair's book, "Precision Reloading & Shooting Handbook 10th edition" 1999, page 88: [measuring resized cases] ".. the dial indiator tip should be positioned so it is bearing right above the midpoint of the neck.

I had assumed that one would seat a bullet and measure the runout at the ogive with the bearing near the front and rear of the body of the case.

Clark said---

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I had assumed that one would seat a bullet and measure the runout at the ogive with the bearing near the front and rear of the body of the case.

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You are measuring the variation in reference to the "bed" of the tool. If the neck is of varying thickness (all factory brass is) the bullet will show eccentric even if everything else is straight.

To measure the concentricity of the *bullet* in relation to the case, you MUST first turn the neck to the same thickness and fireform in a chamber that's also concentric. THEN the measurement taken on the bullet makes sense.

I see no use for a concentricity guage unless your rifle is "right" (tight, concentric, and straight chamber with a BR neck), and the brass prepped by turning and fireforming first.

I agree with JBelk, I feel too many shooters expect case prep to work "Magic" with factory chambers. To prove a point I made 308 cases from 270 win brass, to get enough brass in neck area of rem pss "tactical" chamber. The shooter could not tell when he was shooting "tight cases or standard, I tested to see by telling him he was shooting the good stuff, and his groups shrank(in reality I gave him std stuff without his knowing!)
I use this tactic with pistol shooters quite often.

I have a way to measure the concentricity of the chamber. I put the test indicator in the chamber before I take the barrel out of the lathe when chambering. The measured run out of the grooves to start plus the measured run out of the chamber at the breech is the maximum the chamber can be eccentric [assuming a good reamer pilot fit].
With this method, my 257 RAI chamber is no worse than .001" eccentric.

[ 04-02-2003, 19:48: Message edited by: Clark ]

Concentricity gauges can help even if the rifle is not "perfect," like a regular factory rifle.

Mostly, I have been able to tell if I was making bad ammo!

I have a rifle that would shoot well with facory ammo, but not my handloads. I rolled them on the Casemaster, and realized somethign was seriously out.

The expander rod was bent in the die, but you couldn't really tell. Now the rilfe shoots very well indeed with my loads!

If there is a problem, I'll play with the Casemaster, but I don't use it all the time. I'll check fired brass on the neck first, then resized/trimmed brass on the neck and then I'll check he seated bullet on the ogive.

I know what a Jack is saying- what's the point of putting perfect ammo in a sloppy rifle? But the guages are still fun to play with.