1. ## Concentricty Guage Question?

Question for the knowledgeable:
I have a Sinclair Concentricity guage & am told the dial reading (rotation on the case body) should be halved to determine actual run-out. Is that correct?.....or not?

I'm also told the Hornady guage (because its rotation is from case head & bullet point) gives an actual run-out reading, so is different from the Sinclair. Is that correct...or not?

I'm trying to understand how if the dial pin is measuring from the outside of neck/bullet in both cases, why one can be different from the other.

2. Originally Posted by deeangeo
Question for the knowledgeable:
I have a Sinclair Concentricity guage & am told the dial reading (rotation on the case body) should be halved to determine actual run-out. Is that correct?.....or not?

I'm told the Hornady guage (because its rotation is from case head & bullet point) gives an actual run-out reading, so is different from the Sinclair. Is that correct...or not?

I'm trying to understand how if the dial pin is measuring from the outside of neck/bullet in both cases, how one can be different from the other.
I have to agree there - I don't understand how they differ. Yes, they support the case in different ways but the total measured deflection will be a max/min and run out will be half that on both devices.

3. Originally Posted by 1066
I have to agree there - I don't understand how they differ. Yes, they support the case in different ways but the total measured deflection will be a max/min and run out will be half that on both devices.

That's a damn good looking guage Allan, the rotation wheel seems a very handy device.

I'm not an engineer or mathematician, so the questions I ask are because I'm short in the understanding department!

What I'm reading on the dial then, e.g. .002", really indicates .001" run-out & .004" = .002" !
So does this mean if the accepted standard of good reloaded ammunition is max .002" run-out and my dial reading shows .004" or less, the ammunition is fine, or is it the dial reading should not exceed .002"?

Sorry, not being simple here, but I haven't read anywhere a clarification on this issue.

Checking my case neck/body alignment, I find after F/L resizing, dial readings are usuually max. less than .001" & usually .0005".
(I put this down to brass thickness variation)

When bullet seating, bullet alignment is approx 50/50 (however careful I am) dial readings show .0015" - .006" or more, using the Nosler Accubond bullet.

My seating dies are both RCBS Competition (which I've used for years) & in the last two weeks using a Redding Competition seating die.
Both dies have micrometer dial for accurate OAL, but, I cannot find one performing better than the other in seating concentricity and for some undetermined reason there can be a wide difference in dial readings on the guage.

So I'm looking for clues to making more consistent ammunition rather than half being what I'd consider excellent & the remainder a poor 2nd.

4. Originally Posted by 1066
I have to agree there - I don't understand how they differ. Yes, they support the case in different ways but the total measured deflection will be a max/min and run out will be half that on both devices.

I never use these gauges on my home loads as I only hunt at moderate ranges and plink when at the targets, no BR shooting. If I did start using one I would be proud of making this little gauge,what a nice piece of kit,well done the maker.

It is designed to measure TIR or (total indicated reading)same as trueing up in the lathe. I suppose that is the same as run out, so half the run out to measure how true the bullet seats. Just another part of our obsession with reloading.

5. Well done!
Do you have a set of plans?
It looks like an interesting project for the long, dark winter nights.

6. Thanks for the comments, unfortunately no plans, I just make these things up as I go along. I have, however, made a video of the making which will be posted on my youtube channel when I get it finished.

Run-out with just general purpose shooting ammunition doesn't seem to be much of a problem at modest ranges - more of a problem at ranges in excess of 600 yards when target shooting, especially if you are looking for F-Class or benchrest accuracy at 1,000 yds.

Anything less than .003 would be considered good with many reasonable quality factory rounds in the .005-10 range. Military issue is often .02- .03, this is a clearly visible wobbly if the rounds are rolled on a flat surface.

I remember seeing a video where ammunition from a major manufacturer (Hornady ?) was being graded and packed. A woman was rolling around half a dozen rounds on a table by hand then taking out the visibly wobbly ones - these were then packed in boxes of twenty marked Gold or Silver grade.

One of the causes of bullet run-out is the seating die - even with good quality dies you need to check that the seating stem suits the bullet profile. The bullet shouldn't be pressed home with the tip, the recess in the stem should be deep enough that the tip is completely clear. A faint visible ring round the top of the bullet where the stem is contacting is a good sign. This problem is now not unusual with plastic tipped bullets becoming more common.

Another cause of run-out is the expander ball being dragged out of the case when resizing. Some dies drastically under size then when the expander ball is dragged up the case is unsupported. I have been experimenting with resizing without the expander and then using a plug to expand from the top.

Here's a video of my plug expander:

7. Funnily enough I loaded a batch of Vartarg ammo last night, I checked concentricity of each round and sorted them adcordingly. The plan is to test the best against the worst and see what the real world difference is..
I don't know wether the total deviation should be measured or the deviation from the central axis i.e half the total figure. My two worst rounds had a total deviation of .005...

One thing to consider (and I'd appreciate some input on this) is the relationship between run out and concentricity. My understanding is this. If you had a perfectly circular plate and drilled a hole exactly in the middle the concentricity would be zero. However if the drill bit was not at 90deg to the surface then a run out would be seen when a rod was placed in the hole and the plate rotated.
So a concentricity error would occur when the brass was thicker on one side of the neck than the other, this would show up on the concentricity gauge and the error would be the same where ever on the bullet the gauge was placed.
A run out error would occur when the bullet was not seated square in the neck, a run out error would be larger when measured at the bullet tip and smaller when measured close to the case neck...
have I got this right?

8. Great work on the home made die.
I think the expander on my Vartarg die is slightly off centre when it's done up tight with the locking ring. I have put a lambs tail docking band under the locking ring, it's nice and squishy so it allows a small amount of float, I'm going to try loading some more and see if the concentricity improves.

9. Originally Posted by Tom D
Great work on the home made die.
I think the expander on my Vartarg die is slightly off centre when it's done up tight with the locking ring. I have put a lambs tail docking band under the locking ring, it's nice and squishy so it allows a small amount of float, I'm going to try loading some more and see if the concentricity improves.
I think you are quite correct in your thinking - that's a good description. It would be good to be able to do some meaningful tests to see just how much difference it does make. I think the problem is that any improvements will only show up at longer ranges and with that you get the usual wind influence.

I just try to make the best ammunition I can - I then know it's me or the rifle that's the problem. I've never been able to measure any improvement in uniforming primer pockets and flash holes or weighing the powder accurately, it's just part of making a good round.

Once you start measuring these things you find all sorts of "problems" that you were happily unaware of. The locking ring throwing the die off centre seems quite common, I've had good results using the Lee locking rings, with the "o" ring on my Redding dies.

My thoughts on excessive run-out is that the bullet will act as if it has a lower BC - more drop and drift at longer ranges. A fully concentric bullet, spinning true on it's axis is ideal - a slippery streamlined shape. A bullet that is off centre and spinning at 180,000 rpm must be like a fuzzy blob and produce more drag - just my thoughts.

10. So to be clear, when someone refers to a run out of .004 they are seeing the dial move from +4 to -4?

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