Concentricity gauge build

J

jmorris

New member
There have been a few times I have wished I had a simple little concentricity gauge dedicated to the reloading room for measuring runout in cases and to see how well bullets are being seated, so I built this one today.

There is a slot machined into the base plate that the bearing holders ride in with an extra wide slot under that so the nut plate has clearance. This makes it so I just need one Allen wrench from the top to set it up.

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The bearings are .375 and set into the aluminum carriers with Devon, I used a 1/4" stainless rod to mount one of my indicators to and a 1/4" dowel to locate the back of the case.

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Tested it out on a precision ground dowel and it works but I think I am going to add a spring loaded wheel with and o-ring on the OD to act as a "tire" that holds the case down and back against the dowel and give my fingers something a little larger to turn.

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Almost didn't read this. Then I looked at who posted, knew it would be something good. Always see ingenious work by you. Nice job jmorris.
 
jmorris
SHOW OFF. No really, very nice work. Wish I could build something that accurate. Keep up the great work. Chris
 
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Very cool.
I just use a gauge setup for arrows from my archery days.
Waste not, want not.
Cuts down on the need for garage sales, too.
 
I did something similar a few years ago. I hotglued 4 gage balls in the holes of a 1-2-3 block then anchored my Noga mag base to the end of the block. I can set my .0005" indicator to measure the runout by butting the case ip against the magbase and rolling it on the 4 gage balls. It isn't perfect, but it works okay for sorting purposes if I want to try for a really good grouping or just to check my seating die.

 
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With the 150lb magnet in my Noga it holds the block rock solid. My 6.5x55SE is a tapered case so it is kind of tricky to roll it smoothly but it seems to be working good enough for my needs. I don't shoot competitively or anything.
 
The B&S are my "goto" indicators but I did set it up with a Mahr an a standard to play with it a little. Learned that it is easier with the wheel.

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This will give false readings if the base of the cartridge is not square to the sides and the indicator is reading off the ogive and not the straight portion of the bullet. In other words if the case while spun is moving back and forth due to not being square, then the indicator is reading off a tapered surface. Be sure to place the indicator as close to the case mouth as possible.
I've spun 10's of thousands of benchrest bullets and never reallly seen a difference in group size but these were all seated in precision hand dies.
 
In other words if the case while spun is moving back and forth due to not being square, then the indicator is reading off a tapered surface.
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If the base of the case is not square, even it is straight walled, it will be pushed into the die crooked.
 
It is an either or thing., the case body has the taper or the neck has a taper. And I know, no one understands that.

And then there is the insistence on making gages as Clark suggested:

Looks like a Russian military clone of the Sinclair.
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Again, I have an electronic Pratt & Whitney gage that measured down to .00005", and then I removed the electronics and went with a dial indicator on the contact point. There is nothing about a case that requires a measurement below .001" but JIC (Just in case) I have dial indicators that get down to .0001". And then there is another way to make run out gages, problem; it is not sophisticated enough for reloaders.

F. Guffey
 
Another pretty cool and useful piece of tooling. Before I retired I had a full proto typing machine shop at my disposal as well as some really excellent mechanical engineering and tool and die types. The only thing I miss in retirement is that machine shop, boy did I love having all of that at my disposal and I was electrical engineering. :)

Ron
 
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