Concentricity Guage


Temecula California
Does anyone have one?
Which brand?
How close do you try to get your cast bullets to zero run out?
Friend loaned me one to try out out on some 223 bullets I had reloaded.
Was surprised as to how close some were and out far out others were using the same bullet.
Is there an easy way to correct the ones with large run out other than pulling he bullet and starting over?
Or is this a road into darkness I o not want to travel?



Staff member
All depends on the intended use of the ammo and the firearm firing it. Like a lot of accuracy tricks it can certainly be useful but for plinking ammo and many off the shelf firearms can be huge waste of time. When I was competing I would "roll" my bottleneck rounds for my custom built match grade XP-100's. When trying to hit a target the size of a pack of cigarettes at 200 meters with an iron sighted hand held handgun any advantage can be helpful. When shooting an off the shelf hunting rifle capable of 2 inches at 100 yards it's a waste of time. Bottom line, consider what you can reasonably expect from your gun and what they are intended for. While some things are useful nothing will turn a pigs ear into a silk purse.


West Central AR
The straighter it starts the straighter it flys .........
I'm told it makes a difference and might eliminate an otherwise unaccounted for flier .
I've never really dabbled much in it because I don't really have a rifle nor do I shoot at a level where it matters much beyond an otherwise unaccounted for flier .


Staff member
Mine is from Sinclair. Does everything I need. Well designed and works for any cartridge I will ever shoot.

Great device to see if your dies are making straight ammo


Temecula California
The one my friend loaned me is from 21st Century.
Is a great tool but on the expensive side.
He is a competition shooter so only has he best of everything.
Will look at the sinclair one.
Not sure I need one but never hurts to have another took in the box.



Well-Known Member
I just set the bases on a flat plate and look at the tip of the bullets. Those out of line have a problem. Rimmed cases are hard to roll with any accuracy.
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Springfield, Oregon
I use the Sinclair one as well. A good inline seating die goes a long way for making ammo with very little run out. I like the Forster Ulta Micrometer seating dies. Redding make so nice ones as well.


Well-Known Member
for much of what we do the RCBS unit is good enough.
it also allows you to measure case neck thickness and do a couple of other tasks.
it isn't the greatest or easiest to use, but it will get you close enough to sort ammo and can see the difference on paper.
it will also let you measure fired cases, which is how you find out which rifles have straight chambers and which ones don't.


High Steppes of Eastern Washington
I use one made by a very high quality machinist. Twenty years ago I did a lot of work with it for CBA cast bullet match loads, about 960 rounds in one summer looking for the best reloading dies. A: once the cartridge is loaded and seated, you are wasting your time trying to "adjust it". Only works with resizing the case and starting over. B: Measure the runout on fired cases, as a chamber with 0.004" of chamber runout will not shoot better with bullets with 0.001" runout. FWIW, Ric
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Well-Known Member
They are almost invaluable for diagnosing exactly "where" in your handloading process that any runout is being produced.... once you've figured that out,they sit on the shelf most of the time.

The two times I had bad runout.... once with a set of Lee 22-250 dies,which got replaced with a really nice older set of Lymans. And more recently an RCBS seater for a 223,which led me to make a hybrid seater( "inline" style,but threaded 7/8-14).

Once you learn to use one..... and get good at it.... you'll be able to roll one on a flat plate and tell pretty much what .001" looks like. Mine is based on a Brown & Sharpe 730 that we sorta "grew out of" in the machine shop(use a much bigger version). Fabricated the V blocks out of some bronze repurposed from commercial door lock "keepers". Use sheet metal to square and space them. Oh yeah,I don't straighten loaded rounds. Figure out where it originated.
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Well-Known Member
They are almost invaluable for diagnosing exactly "where" in your handloading process that any runout is being produced.... once you've figured that out,they sit on the shelf most of the time.
Exactly. Figure out WHICH process is screwing the pooch, and fix it. Resizing dies that cram the necks down too small and then yank an expanding ball back through is suspect #1, I hone necks or use bushing neck (or FL) dies such as RCBS gold medal match dies. Over-sizing necks, dragging the ball back through, and then using a two-diameter cast bullet expanding die like Lyman makes does murder to case necks, and they will always stretch toward the thin side. Wobbly press rams or shellholders out of alignment with the die at any part of the stroke are another major issue (cough cough LEE TURRET cough ahem). As was mentioned by a couple of people, an in-line seating die (I swear by Forster for standard reloading presses, Sinclair for hand-seating), combined with no more than .002" for neck tension will go a long way toward seating your bullets straight, concentric, and true.

I use a granite platen and Mk 1 eyeball to check runout most of the time.


Well-Known Member
didn't someone include a little hole in the side of their stand so you could try to straighten the round?
I doubt you'd ever get it close with that, and I know putting it back in the die again won't do it either.
I usually mark a box for anything crooked, and even segregate anything near .003 if I think it's gonna matter.
I make sure to shoot the crooked ones and re-look at the cases afterwards.
a good rifle will shoot a case back to straight, you have to figure out how to keep them that way.