Help with a sinclair concentricty gage

[wanttobe]

I have been using my gauge for some time now but saw some pictures of the gauge and it showed the loader brass seated on both the bearing blocks and the dial indicator pin touching the bullet at the OG. I have always had the brass on the rear block and the bullet on the the front block without the brass touching the front block. My question is what is correct? And does anyone have any good tips on using this gauge? Thanks

 

[Lone Hunter]

This is how I use mine

 

[BoydAllen]

Of course you can use it any way that you want, but....I have always used my gauges with the front block balls making contact on the case as close to the shoulder as possible, with the indicator reading off of the bullet, about where the rifling would make contact.

 

[T-shooter]

It's important to hold the case against the ball bearings tightly and a little lube on the balls also helps. I usually check here. .001" or less is great, .002 is good, and more than that, I try to straighten and if unsuccessful, use them for fouling/warmup shots.

 

[Bart B.]

With that setup, any run out on the case body by the shoulder will read about 50% more on the dial indicator. Assuming there's no run out on the case near its pressure ring.

Too bad that such gauges don't center the case shoulder in a round hole (about shoulder reference diameter) like they are in the chamber when the round fires.

Easy to make.

 

[dstoenner]

I have a Accuracy 1 concentricity gauge with the big wheel. IMO if you want measure concentricity you should measure it on the straight part of the bullet not the curved part. If you measure it on the curve, part of the variance will be due to changes in the curvature of the bullet. So you won't be getting a true measurement. YMMV.

I agree with everything thing said. To add a little more if you have case heads that have divets in them because of extractors or ?? Then when that divet hits the rear reference pin the case moves foward and you then see the needle move alot and you have to wonder is it really that much or .. If you are on the bearing surface of the bullet you will not seevthe dramtic swing of ghe needle

David

 

[wanttobe]

Thanks for all the replys, When I have the loaded round on both bearing blocks and the pin on the bullet I will get a movement or deflection of about two indicator marks but the same round will measure less movement with the brass only on the rear block and the bullet on the front block. I also have a problem when rolling the round trying to keep it smooth as it moves. Does anyone have a better process for moving the round with out a lot of jumping?

 

[Bart B.]

When I have the loaded round on both bearing blocks and the pin on the bullet I will get a movement or deflection of about two indicator marks but the same round will measure less movement with the brass only on the rear block and the bullet on the front block.

That's normal.

Put the case on the bearing blocks then dial indicator near bullet tip.

Have everything clean to prevent the needle from 8jumping around.

 

[Uncle Ed]

I have both gauges below and they hold and rotate the case in different ways. And the Hornady gauge care how much coffee you drink and how much your hand shakes.

For simplicity sake the Hornady gauge holds the case like a full length size case would be held in the chamber. Meaning the rear of the case held in the recessed bolt face and by the bullet in the throat, and the body of the case not touching the chamber walls.

With gauges that spin on the case body and if the case body is egg shaped you will have more indicated runout. I think of these type gauges better for neck sized cases where the case body can have a effect on bullet alignment. Meaning if you have unequal case wall thickness the case can bulge on the thin side and become egg shaped.

Bottom line, practice finger Yoga until your spinning finger reaches Zen and then you will have a total state of rotational enlightenment.

 

[Bart B.]

For simplicity sake the Hornady gauge holds the case like a full length size case would be held in the chamber. Meaning the rear of the case held in the recessed bolt face and by the bullet in the throat, and the body of the case not touching the chamber walls.

I totally disagree with that concept. It implies all bullets are seated to push into the throat. It ignores case shoulders hard centering in chamber shoulders. And extractors pushing the back of case bodies against chamber walls.

Did Hornady say that?

It holds cartridges about like the top one in the picture.

 

[Uncle Ed]

I totally disagree with that concept. It implies all bullets are seated to push into the throat. It ignores case shoulders centering in chamber shoulders. And extractors pushing the back of case bodies against chamber walls.

Did Hornady say that?

All bullets end up in the throat when chambered and its up to the reloader to set how far off the lands. And the average throat or freebore is .001 larger than bullet diameter. (.0005 ON EACH SIDE OF THE BULLET) So I would say the bullet centers the case shoulder and not the other way around.

Below Mr. Salizar is answering a neck sizing and partial full length resizing questions. And why full length resizing gives the bullet more wiggle room to be self centering in the throat. (The cartridge should fit the chamber like a rat turd in the violin case)

The Rifleman's Journal
Germán A. Salazar

"a full-length sized case in which the neck is also fully sized. There is clearance at the neck and in the body of the case, the closest fit anywhere is the bullet in the throat. If the neck to bullet concentricity is good (although it needn't be perfect), then the bullet will find good alignment in the throat and the case body and neck will have minimal influence. Let's not forget that the base of the case is supported by the bolt face or the extractor to a certain degree as well; this is yet another influence on alignment. As you can see, there are several points from base to bullet that can have an effect. My procedure is to minimize the influence of those that I can control, namely the case body and neck, and let the alignment be dictated by the fit of the bullet in the throat and to some extent by the bolt's support of the base. Barring a seriously out of square case head, I don't think the bolt can have a negative effect on alignment, only a slightly positive effect from minimizing "case droop" in the chamber. Given that a resized case will usually have a maximum of 0.001" diametrical clearance at the web, this isn't much of a factor anyway.

In conclusion, I believe that allowing the bullet to find a relatively stress-free alignment in the throat by full length sizing (including the neck) and turning necks to enhance concentricity gives the bullet the best probability of a well-aligned start into the rifling."

 

[Bart B.]

I use SAAMI's definition of throat; the angled origin of the rifling in front of the freebore. Also called leade.

The average freebore diameter in SAAMI specs is several thousandths bigger than bullet diameters as bullets have a .003" diameter spec.

Custom stuff may be different.

Salazar ignores the case parts having the greatest effect on centering bullets to the bore when fired; he has well centered on shoulders. But then, most people do the same.

 

[Uncle Ed]

The OP is using a Sinclair concentricity gauge and the case body spins on the gauges ball bearings.

But how many reloaders put the gauge on the case body and see if the case body is egg shaped and causing more indicated runout on the bullet.

So what does spinning the cartridge on the case body prove if you full length resize and the case body doesn't touch the chamber walls.

It may seem like a silly question, but to me spinning the cartridge on the case body would apply more to people who neck size only. Meaning the case body having more guiding effect on the bullet and the alignment in the throat.

 

[Uncle Ed]

I use SAAMI's definition of throat; the angled origin of the rifling in front of the freebore. Also called leade.

The average freebore diameter in SAAMI specs is several thousandths bigger than bullet diameters as bullets have a .003" diameter spec.

Custom stuff may be different.

Salazar ignores the case parts having the greatest effect on centering bullets to the bore when fired; he has well centered on shoulders. But then, most people do the same.

So what centers the bullet below, the case shoulder or the bullet. Sorry a little bullet runout humor. But if you have .003 bullet runout what centers the bullet in the throat, the shoulder or the bullet. How much case shoulder runout are you allowed? (more runout humor)

So Look at line (G) below and tell me what the diameter of the throat is in a SAAMI chamber.

 

[Bart B.]

So what centers the bullet below, the case shoulder or the bullet.

Neither.

A sledgehammer closing the bolt into battery may do it.

 

[Bart B.]

So Look at line (G) below and tell me what the diameter of the throat is in a SAAMI chamber.

Throat diameters: .219" at the bore back to .224" at the chamber mouth. There is no freebore.

 

[Ned Ludd]

If the bullet is rolling on the front block, all you're measuring is the concentricity of the bullet itself, not the loaded round. The case should roll on both blocks with the bullet unsupported as shown in the picture/tube posted by Lone Hunter in the 2nd post.

 

[Bart B.]

But if you have .003 bullet runout what centers the bullet in the throat, the shoulder or the bullet.

Shoulder with the neck's back centered on it with no throat touching the bullet. Bullet tip will be a bit off bore center if the neck is crooked to the case axis as typically shown with bullet runout

Its called the Dixie Cup Syndrome. Two identical shoulders pressed together align on the same centerline.

 

[Bart B.]

How much case shoulder runout are you allowed? (

Zero is best.

Neck run out is usually the culprit. It takes the bullet with it. Bullets typically point where necks do.

Best measured with the shoulder in a hole at or near reference diameter.

I don't like the concept that pressure on the bullet to straighten it will not change the neck's grip on it. Especially with minimal neck tension to start with.

 

[Uncle Ed]

Neck run out is usually the culprit. It takes the bullet with it. Bullets typically point where necks do.

So the case shoulder can't center the bullet in the throat if you have any neck and bullet runout.

Below the bullet is rubbing the chambers throat and your Dixie cup within a Dixie cup isn't working.

Below the .223 has a throat diameter of .2245 or .0005 larger than the bullet. So what happens if you have .002 or .003 bullet runout with .0005 bullet clearance in the throat.

I think your Dixie cup hat in the Navy has effected your judgment.