Author Topic: First a homemade concentricity gauge, then bought a concentricity gauge  (Read 5230 times)

Tyler Durden

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Hi all....

Yeah, yeah, long time no see...

Pardon me if this thread seems like spam.  I am in no way associated with these people.

I was wondering why my .223 reloads/handloads weren't grouping any better.

Some thoughts entered my mind wondering if it wasn't a concentricity or bullet runout issue.

So at first I made my own concentricity gauge out a small block of steel and 4 things of slingshot ammo.  The I used a magnetic base and a dial indicator.

You can watch my initial trials here:

I was kinda shocked by the results, so I splurged, and bought a very high end concentricity gauge:

That is like 7 to 8 thousandths of runout (0.007 to 0.008).

So to have something to compare against, I used a round of factory ammunition.  All I had around was some Black Hills ammo:

Which shows about a thou to 1.5 thousandths in runout.

Soooo....when I get some free time, I will have to dig deeper into my press to figure out why the actual bullets are getting seated crooked.  It is a Dillon 650 auto indexing progressive press.  I had noticed previously that the shellplate wasn't stopping in the right position. 

And no, I am not here to foster this idea that a single stage press is inherently better at reloading rifle ammo.

If you are wondering why your handloads aren't more accurate than factory ammo, you could always try building your own concentricity gauge.


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Fun to try out your own "tools"  then compare it to the commercially made stuff.

I don't reload rifle stuff because I just didn't want to worry about things like this.
Will work for ammo
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Excessive run-out can be caused the resizing die.  Also, during the bullet seating process.
Yes, I use a single stage press, but it does give me the chance to monitor the whole process.
When resizing, are you lubricating the inside of the case neck?  If not, try using a carbide button expander. They do work. I use the RCBS competition dies, which allows me to place the bullet inside the die through a window in the side of the die.  I use this type of die on .308 win, This helps align the case to the base of the bullet. This is really important if you use flat base bullets.
And I ALWAYS seat and taper crimp with separate steps.
Check the run-out on a fired case, and a resized case without a bullet seated, of the case necks.
Also, check that the case lengths after resizing are the same. I hold all of my cases to within .002 overall of all cases of a length at the low end of the cartridge specification.  These are the easiest steps to control, and I have less than .002 run-out, if I am being picky.

Tyler Durden

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I am...or rather I was buying pre-processed brass from a guy local to me.  He was buying brass off the government liquidation auctions.  Then once he got it back here, he was using an automated Dillon 1050 to resize, trim, and de-crimp the crimped in primers.

Last night, I took alike 3 or 4 out of the thousands of brass I bought off him.  Each of those empties had some runout at the neck.  At most, I saw 8 thou, the least I saw was 0.003 in runout.

So my best guess is he didn't have something set right with his resizing die.  If it had an expander ball on the decapping rod assembly, then it was pulling the case necks out of round.... as the expander ball got pulled back through the case mouths.

I have an extra toolhead for my 650 set up with just the RCBS X sizer die.  It doesn't use an expander ball, but rather a mandrel.  I ran those 3 or 4 cases up into the X die.  Then I put back on the cincentricity gauge.  That knocked the runout to 0.002 or less. 

That made me happy that I figured out the problem...then figured out a solution.


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