Using the Hornady Concentricity gauge

deepcore · January 10, 2011, 04:07 PM

Just started playing with my new Hornady Concentricity gauge.
Had a question:
After finding the lowest reading on the gauge for a cartridge...setting the dial face so that that point is "0"...measuring the current run out...doing the adjustment...and then re-measuring the run out.
At this point if the dial is deflecting only .0001 (for example) BUT it's not deflecting from .000 to .001 but instead deflecting (for example) from .0004 to
.0005...is that a .0001 run out?
Do you have to keep re-zeroing the gauge face after each adjustment?
Because I started rezeroing each time but found that after seeing that the needle would still only move the .0001 began to wonder if doing that many re-zeros was needed.

wogpotter · January 10, 2011, 06:26 PM

What you are seeing is the difference between "absolute measurement" & "relative measurement". As you've figured out the moment is the same, but it is not movement from zero.

As long as you don't have a problem with doing the math you don't need to re-zero, just calculate the maximum - the minimum for a total. The time I find this difficult is if I get into negative numbers, from -.002 to + .01 is a PITA to calculate. I use an RCBS which has "flags" on the dial gauge. What I do is set flag 1 to min & flag 2 to max & see if the needle stays within the limits I've set.

BTW if you can get a .0001 run out I want to sit at your feet & learn from you as I've never gotten that close myself.

deepcore · January 10, 2011, 07:09 PM

I was thinking it was all relative.
When I called Hornady to verify they said you could keep re-zeroing as you go.
Which would make it relative right? Because the point of reference is moving.

For it to be absolute you'd have to leave the zero where it is and adjust the round so that it will only wiggle from .0000 to .0001 (in an almost perfect world) to .0002 or whatever without changing where the zero is.

Almost like setting it for a "perfect" round and adjusting all your other rounds to the ideal.

Or I'm totally wrong and just need more time to get it straight in my head.

Meantime next step for me is to magic mark the case so I have a better visual frame of reference as to where the high and low "spots" are on a round and how they relate to the needle movement and where the adjustment screw is applying the correction.

swmike · January 16, 2011, 06:47 PM

All my ammo, for the most part, has less than .002 runout and some as little as .0005 right out of the die.

The gauge is of course verifying this and there HAVE been a couple that did exceed .004.

Correction is a piece of cake. The first results at the range were very encouraging. Absolutely no "fliers" at 300 yards. Was too darn cold to stay very long but was able to keep a nice tight group of 20 within a 1" circle.

Certainly easy to use once set up and the setup is not hard at all.

wogpotter · January 16, 2011, 08:41 PM

That's where it gets confusing.
Think of it this way.
Relative= displacement relative to a different point of measurement.
Absolute= absolute moment from a benchmark (in this case zero).

Its kind of academic as long as you can figure out the change. The change is what you want to measure as in "How much does my load move relative to other positions as it is rotated about it's axis". As you don't seem to have any problem doing this why bother to constantly re-zero?

January 10, 2011, 04:07 PM	#1
deepcore Senior Member Join Date: July 24, 2010 Posts: 364	Using the Hornady Concentricity gauge Just started playing with my new Hornady Concentricity gauge. Had a question: After finding the lowest reading on the gauge for a cartridge...setting the dial face so that that point is "0"...measuring the current run out...doing the adjustment...and then re-measuring the run out. At this point if the dial is deflecting only .0001 (for example) BUT it's not deflecting from .000 to .001 but instead deflecting (for example) from .0004 to .0005...is that a .0001 run out? Do you have to keep re-zeroing the gauge face after each adjustment? Because I started rezeroing each time but found that after seeing that the needle would still only move the .0001 began to wonder if doing that many re-zeros was needed.

January 10, 2011, 06:26 PM	#2
wogpotter Senior Member Join Date: September 27, 2004 Posts: 4,811	What you are seeing is the difference between "absolute measurement" & "relative measurement". As you've figured out the moment is the same, but it is not movement from zero. As long as you don't have a problem with doing the math you don't need to re-zero, just calculate the maximum - the minimum for a total. The time I find this difficult is if I get into negative numbers, from -.002 to + .01 is a PITA to calculate. I use an RCBS which has "flags" on the dial gauge. What I do is set flag 1 to min & flag 2 to max & see if the needle stays within the limits I've set. BTW if you can get a .0001 run out I want to sit at your feet & learn from you as I've never gotten that close myself. __________________ Allan Quatermain: “Automatic rifles. Who in God's name has automatic rifles”? Elderly Hunter: “That's dashed unsporting. Probably Belgium.”

January 16, 2011, 06:47 PM	#4
swmike Senior Member Join Date: June 25, 2005 Location: Marysville, WA Posts: 670	I just bought one and am disappointed. All my ammo, for the most part, has less than .002 runout and some as little as .0005 right out of the die. The gauge is of course verifying this and there HAVE been a couple that did exceed .004. Correction is a piece of cake. The first results at the range were very encouraging. Absolutely no "fliers" at 300 yards. Was too darn cold to stay very long but was able to keep a nice tight group of 20 within a 1" circle. Certainly easy to use once set up and the setup is not hard at all. __________________ My definition of Gun Control--- A steady grip and hitting your target. "In God we trust, all others are suspects." "If I shoot all the ammo I am carrying, either I won't need any more, or more won't be of any help". ____________________________________________

January 16, 2011, 08:41 PM	#5
wogpotter Senior Member Join Date: September 27, 2004 Posts: 4,811	That's where it gets confusing. Think of it this way. Relative= displacement relative to a different point of measurement. Absolute= absolute moment from a benchmark (in this case zero). Its kind of academic as long as you can figure out the change. The change is what you want to measure as in "How much does my load move relative to other positions as it is rotated about it's axis". As you don't seem to have any problem doing this why bother to constantly re-zero? __________________ Allan Quatermain: “Automatic rifles. Who in God's name has automatic rifles”? Elderly Hunter: “That's dashed unsporting. Probably Belgium.”

January 10, 2011, 07:09 PM	#3
deepcore Senior Member Join Date: July 24, 2010 Posts: 364	I was thinking it was all relative. When I called Hornady to verify they said you could keep re-zeroing as you go. Which would make it relative right? Because the point of reference is moving. For it to be absolute you'd have to leave the zero where it is and adjust the round so that it will only wiggle from .0000 to .0001 (in an almost perfect world) to .0002 or whatever without changing where the zero is. Almost like setting it for a "perfect" round and adjusting all your other rounds to the ideal. Or I'm totally wrong and just need more time to get it straight in my head. Meantime next step for me is to magic mark the case so I have a better visual frame of reference as to where the high and low "spots" are on a round and how they relate to the needle movement and where the adjustment screw is applying the correction.