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Concentricity gauge

 
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  #8  
Old 12-15-2009, 10:12 PM
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Re: Concentricity gauge

The H & H looks similar to the new Hornady



I have some experience fixing runout with the Bersin



with it you push on the bullet but like Robster shouted at us, you are mostly just canting the bullet, or perhaps uncanting it. The Bersin is a good runout reducer, not a runout eliminator. There is a trick to learning just how hard to push on the bullet just enough but not too much. If you push too much then you will have to go to the other side and push it back. Many times you can go round and round pushing here and there and just chasing it around until you loosen the bullet in the neck. Soft case necks will push easier than work hardened ones.

The most useful purpose of concentricity gauges is to show you what you are doing that is reducing or creating runout in your sizing and prep procedures. Once you have a system down and buy the best cases with the least amount of variation in neck thickness, size with a die like the Lee Collet that does not create runout, size with a die like the bushing die in combination with neck turning and use a Competition Seater with a seating stem that fits your bullet, then you can fine tune your procedures to not have runout in the first place.

However the H & H, Hornady or Bersin will reduce runout somewhat, generally 50% to 75%.

Just my experience, YMMV
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  #9  
Old 12-16-2009, 11:38 AM
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Re: Concentricity gauge

I am not a user nor do I plan on using one of these. However, the one Mo has is a very very well made piece of equipment. I put a brake on an encore barrel for Mo the other day. When he stopped by to pick up the barrel he showed his new toy to me. Very impressive workmanship and design.

I think than measuring concentrically is kinda like chicken soup for a cold. It cannot hurt anything and if it makes you feel better do it.
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  #10  
Old 12-16-2009, 01:18 PM
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Re: Concentricity gauge

Woods,
I did not mean to shout I stink at typing and use the hunt and peck method and usually just leave the cap lock on.
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  #11  
Old 12-16-2009, 03:06 PM
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Re: Concentricity gauge

I should have said it's 'tricky' as there is no malice in it.
And this is where it get's tricky;

Concentricity is taken only to CENTER axis.
If I alter something .001" from concentric, it would measure .002" TIR at the same point.
However, CENTERED ammo as measured isn't always so chambered, because it isn't always straight.

Cartridge total indicated runout[TIR] combines factors; banana shaped cases, offset necks, thickness variance, seating misalignment, and relative measurement errors. When we subtract our minimum reading from the maximum and take the absolute value, the result is our Total Indicated Runout.

The best we can get is STRAIGHT ammo, and TIR quantifies this better than concentricity (given available methods of measurement).
Load a round with zero TIR(straight) and it is concentric.
Load a concentric round, and TIR could still be ugly(not straight).

The best tool I'm aware of to measure TIR(and I've tested a few including H&H), is Sinclair's: Concentricity Gauges - Sinclair Conc. Gauge w/ Digital Indicator
They refer to it as a concentricity gauge, but it's actually a runout fixture, and does not measure concentricity at all. That's ok though, it works. And I can tell you that your ammo(concentric or not) is NOT straight until measured so on this Sinclair(or variant of).
So what is the difference?

Picture your bent ammo as a jump rope, with both ends pinned as typical.
To best define it's maximum displacement from straight, you'd place an indicator in the center of it's arc and measure TIR. Right?
You wouldn't put the indicator nearest one pinned end, as it would show lower runout than maximum(actual). Unless, you don't care about runout, and just want any indication off concentric. Let's say concentricity that you can adjust with pressure on bullet's seated....
So what about runout? What about getting the ammo straight?

Now back to the jump rope. Only this time you pin the center of arc, and one end slid to the same plane, and indicate displacement nearest the free end.
Now your showing every bit of the devil in it, and this is what the Sinclair does.
Your ammo is NOT straight until it measures low enough in runout, with this method.
Is it then concentric as well?
Yes, of course.

Consider a bit of what bent ammo does when chambered(concentric or not)..
Will it be aligned with the center axis of your bore? NO, IT NEVER WILL BE.
How do you get your ammo to consistently point(wherever it does)?
You make it the same,, STRAIGHT

Last edited by Mikecr; 12-16-2009 at 03:16 PM.
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  #12  
Old 12-16-2009, 07:51 PM
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Re: Concentricity gauge

Quote:
Originally Posted by Mikecr View Post
Cartridge total indicated runout[TIR] combines factors: banana shaped cases, offset necks, thickness variance, seating misalignment, and relative measurement errors. When we subtract our minimum reading from the maximum and take the absolute value, the result is our Total Indicated Run-out.
Excellent write-up, Mike. Hopefully others will use it to their advantage.
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  #13  
Old 12-16-2009, 11:46 PM
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Re: Concentricity gauge

Quote:
Originally Posted by Mikecr View Post
Don't let this trick fool you..
Think about it a bit

Mike--no tricks involved it works.
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  #14  
Old 12-18-2009, 11:44 PM
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Re: Concentricity gauge

Depending on the gage and how its used, a given cartridge will produce different numbers. I found this out checking several out one day.

I made my own gage that rests the bullet 1/4 inch up from the head and at midpoint on the shoulder. The dial indicator's tip touches the bullet about 1/10th inch back from the tip.

Best example of what 3 to 4 thousandths of bullet runout measured as above will do happened some years ago. Several thousand rounds of .308 ammo loaded on two Dillon 1050's had their powder charges metered to 3/10ths grain into primed, new Winchester cases. 20 random rounds were tested at 600 yards in one session, group was 2.7 inches. From a standard SAAMI chamber. A couple dozen top shooters from around the world agreed it shot about 1/2 MOA at 600 yards from their rifles.
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