Rcbs case master or sinclair concentricity gauge..

[1stmar]

Just looking for opinions and experiences on these two tools.. Looking to purchase a new tool. The case master had a couple of poor reviews.. Sinclair stuff is usually pretty solid.

[Clark]

I made a one minute video on modifying my Sinclair concentricity gauge.
You can see it operate.
https://www.youtube.com/watch?v=zWHE3ArWpN0

[1stmar]

Thanks Clark...a v block design would probably avoid that issue, no?

[Clark]

I guess.
I just gave my anecdote.
That's nearly the bottom of my shallow well of knowledge
My advice is to avoid expander balls and save the cost of a concentricity gauge.

[1stmar]

I use redding body dies and lee collet dies. But I'd still like a way to measure ro.

[cw308]

Did you look a the Hornady LNL concentricity gauge. Works for me, also corrects runout.

[1stmar]

I have, I'm looking for a way to measure ro near the meplat as well as case thickness.

[Unclenick]

Take a look at the NECO gauge. I have one and zero complaints. It was designed by the late Roger Johnston. He was the first to put an extended anvil (chord anvil) on a gauge design to measure case wall runout back near the pressure ring, where it's usually twice as bad as at the neck wall.

[Bart B.]

Unclenick, it's interesting you mentionig the NECO gauge measuring the case at its pressure ring. That ring's typically got the most out of round measurements on the case. When it's where the case rests against a V block when rounds are spun, whatever runout is at that point will be mixed in with the normal but much smaller out of round at the case body next to its shoulder.

With rimless bottleneck cases the case body runout at the shoulder matters little because the case body at that point is typically clear of any contact with the chamber body all the way around at that point when the round fires. The only part of the case body touching the chamber is the pressure ring where the extractor pushes it against the chamber wall.

[1stmar]

Thanks unclenick, I noticed it says it can measure wall thickness,mean you use this to check for the beginnings of case head seperation?

[Clark]

If I do an google image search for this pic of a 1960 bullet tilt gauge, I get nothing.
If I go to the NRA publications reprints web page
http://www.nrapublications.org/
I get nothing when searching for
"Gauging Bullet Tilt"
THE MOST PRECISE AMMUNITION
FROM A LOT CAN BE SELECTED
WITH A BULLET ALIGNMENT GAUGE.
By A. A. ABBATIELLO
Nor from fragments.
Judging from the content and where I found it in a 1981 NRA compilation of American rifleman articles, it was written ~ 1960

If I do a google search for mentioning the tittle on the www, the first is me in 2004.
Lots of searches on this topic come back to me, Uncle Nick, and Bart.
Way back when I used a program that read text in images and scanned the text. I have over the years posted it on forums no longer in existence or I am no longer willing to link.
I don't know how much I can post of it here.

[Unclenick]

Clark,

Sorry, I accidentally deleted the attachment thinking it was your article link. The article remained, so it wasn't. If it was not copyrighted stuff, go ahead and put it back.

Unfortunately, that A. A. Abbatiello article is still under valid copyright, so it needs permission to be reproduced here. I contacted the NRA almost 3 years ago asking for permission to use it, but they said they couldn't give it because the Author may have the copyright. They don't actually know, because it's so old it precedes their computerized records. They said they would try to find the author or the inheritors of his estate to ask, and get back to me if they could locate them, but they never have. So, apparently, there's no way to get permission at this time. That means we are limited to the general Fair Use doctrine limitations of quoting to a few sentences or maybe a paragraph or two if it is all directly and educationally germane to the subject. The whole article goes too far, though.

That said, the data in the article cannot be copyrighted and you can create your own illustrations and formulas from it. Below, the group on the right illustrates Abbatiello's result from tipping bullets, alongside one for a flat base and stubbier bullet group shot by Harold Vaughn by shooting 8 rounds while indexing the high side of the tilt 90° for each shot. I used Abbatiello's data to show what his experimental results revealed for the longer M1 Type bullet in .30-06. It makes sense because the longer the nose shape, the further the center of mass is from the center of tilt.

[Clark]

Here is the pic again.

I always thought that A. A. Abbatiello was a made up name to get to the top of alphabetical order, but doing those searches today showed that he was into many things back in the 1960s including patents.

[Bart B.]

With 3 or more different cartridge reference and measuring points, there's about a 40% spread in runout a given round will show.

[Unclenick]

That's why I prefer the angle as a measure and not x number of thousandths of tilt. That number changes depending on where the cartridge is supported and where the dial indicator is and how deeply the bullet is seated. Only the angle is constant throughout.

For bullets bending from the root of the case neck, here is how the angle is figured for a few of them.



If Abbatiello was patenting things, perhaps he can be tracked for permission that way, independent of the NRA's attempts.

The one flaw in the article is it lacks allowing for how standard deviations interact, which means he could have underestimated the effect in his case. It just depends on how he measured it. Could go either way.


1stmar,

The chord anvil is really for measuring case wall thickness runout just in front of the pressure ring. It's a little wide for best sensitivity for finding pressure ring thinning. A dental pick or an O-ring pick or just a bent paperclip is sharper and easier to find it with.

[Clark]

My contention is that if the bullet touches the lands, it is centered there.

To be parallel and concentric with the bore, the bullet must be centered somewhere else along the bore line.

When the firing pin pushes on the primer, the case moves forward until the tapered shoulder of the chamber stops the tapered shoulder of the case.

1) If the chamber shoulder is concentric with the bore line....
2) If the case shoulder is concentric and parallel with the inside diameter of the neck....

Then the bullet will be concentric and parallel with the bore in two places and we should have no bullet tilt inaccuracy.

How do we test that condition 2) is met?

We use a concentricity gauge with bearing points a) as far back as possible and b) on the shoulder of the case, and c) put the indicator on the bullet just in front of the case.

And that is why I cut up my Sinclair concentricity gauge with the mill and files in the video at the top of this thread.

[1stmar]

If using a controlled feed type bolt, wouldn't the interaction between the claw and the case rim have an impact on the angle in which the case shoulder touches the chamber shoulder? Maybe there's enough play there where it isn't a factor?

[flashhole]

Clark, did modifying the Sinclair tool give you the capability you were seeking?

[Bart B.]

1stmar, yes, the extractor pushes the back end of the case against the chamber wall. The case back end will be a thousandth or two off center because the case diameter at that point's smaller than chamber diameter. But that's no big issue because the amount's totally repeatable from shot to shot. The bullet tip is about half that much off center in the opposite direction in the chamber where the rifling starts, but that's also repeatable.

The only part of a perfectly straight round headspacing on its shoulder that's precisely centered in the chamber is the case shoulder that perfectly centers in the chamber shoulder when the round fires. A .308 Win. round whose back end is .002" off center in the chamber is at an angle of about 42 MOA, 7/10ths degree from the chamber axis.

[1stmar]

Ok need someone to validate my trig ... Been along time..

Tir=.003
A= 1.174
B=2.00
C=.783

Atan [.003/(2x.783)]+atan[(.003x1.174)/(2x2x.783)]
Atan[.003/1.566)+atan[(.003522)/(3.132)
Atan[.001915]+atan[.00125)
.001915+.0011249

Bullet tilt angle =.00303

[Bart B.]

.00303 degrees?

That's .1818 MOA.

[1stmar]

I take it from your response you think there's something wrong?.. Those were my measurements, is the math wrong?

[Bart B.]

Just wondering if it's minutes or degrees you calculated; looks like degrees. Haven't done the calc's myself.

TIR runout of .003" means bullet runout from straight is .0015". Half TIR.

[1stmar]

My bad I should have indicated I am using the first formula for bullet angle not ro (2 contact points Hornady concentricity gauge). I believe it is in degrees of angle. Using uncle nicks formula above. I don't know how that translates to ro.

[Unclenick]

1stmar,

Your calculator is working in radians rather than degrees. If you work in degrees, the answer is 0.174… degrees.

If you used Excel, you need to run the degrees convertor function. Substituting your data cell addresses for A, B, C, and TIR (you can name your cells after the letters and TIR, except C is an invalid cell name), it would look like:

=DEGREES(ATAN(TIR/(2*C)+ATAN((TIR*A)/(2*B*C))))


Clark,

That bullet contact alignment should work, and it generally works at least pretty well with tangent ogive bullets. But there have been exceptions. Berger found out some time back that secant ogive bullets don't always play nicely seated to touch the lands.

Originally Posted by Berger

For years we have relayed that it is best to jam the VLD into the lands for best performance. This works for many rifles however there are many rifles that do not shoot the VLD well when the bullet is jammed…

… VLD bullets can be sensitive to seating depth and it has been found that these bullets shoot best in a COAL “sweet spot”.

For more of their information and their tuning approach, read the third and fourth paragraphs under the heading VLD BULLET DESIGN, about 3/4 of way down this page.

When they get the right amount of tuned jump, they will shoot, but then you need to produce a coaxially straight cartridge or you need an intentionally maximally tilted bullet (about 0.5 degrees), with either the high or low side marked on the case (your choice, but it has to be consistent) so you can fire with the mark indexed to the same location in the chamber every time.