concentricity gage questions

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nilescoyote

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While I have reloaded for several years I am new to the precision reloading for the long range venue.

I purchased a new sinclair concentricity gage and decided to check some of my reloads as well as some Federal match to base my findings. I was checking bullet run out and got some surprizing results. These are all for 308 winchester.

First I checked some loads I had reloaded on lake city brass that had been full length resized and loaded with sierra 168 bthp. Run out measured from .003 with most being between .005 and .009

Then I checked some Federal match also 168 bthp, run out was between .001 and .009 with the most right around .005-.007

So last I checked some reloads using federal match brass and again 168 bthp and these were .001-.007 with most in the .001-.004 range.

So my questions are, is this normal for factory match ammo? It seems my reloads are right inline with what they are producing. The loads made with lake city brass show the most run out. If I neck turn these will it improve the results. What is the best way to reduce run out?
 
I'm one of those disciples of the Lee collet neck sizing die.

It works because the mandrel which the die squeezes the neck against is also a decapper (though I deprime separately) & thus locates pretty damn close to concentric with the case because the bottom end is aligned by the flash hole. It can be a real bugger to get set up & the instructions don't help all that much, but once you have a handle on it, it's amazing how straight you can load ammo with it. I expect to get no more than .0015" runout measuring near the tip of a 210 SMK or Berger loaded to 3.15" OAL.

One of the other benefits it offered is that the collet squeeze is inwards towards the mandrel, without any downward force, so the die doesn't upset the body of the case at all. That means that I don't have to bump the shoulders back very often, if at all, like I used to whatever other style of necking die I used. That can be a big plus in a factory rifle, where proper body fit in the chamber can minimise the round going cocked through those generous factory throats.
 
I agree with John.Basically the case from from your chamber,once fired,is as straight as its ever going to be for that particular gun.The less reforming during reloading you do to it the better,which usually means neck sizing only if you can get away with it.Once the shoulder has to be bumped or the body resized,run out will obviously increase somewhat.
There is a tool available which is pretty popular with some shooters that will let you adjust your run out (bullet not neck) at the expense of varying your neck tension slightly.I have a friend that uses this tool on every round he loads for his factory chambered sendero and has no complaints at the target.

http://www.kinneman.com/web/2003/catalog/css/catalog_49.html
 
Even if the outside of the case has zero runout, a loaded round will have runout on the bullet equal to the runout in neck thickness (best case), because the ID of the neck is off center relative to the OD. Any runout beyond that can be attributed primarily to the use of an expander ball, which produces enough pull on the shoulder to cause it to yield slightly, asymmetrically, cocking the neck relative to the body of the case. The other cause of runout is excessive reduction in body diameter by full-length sizing combined with body wall runout. If you need to FL size, a body die can be used with a Collet Die in a two-stage process, or a bushing die, or a custom one-piece die to reduce the amount of runout. I think that you would be better off fixing the problem a the source, by using brass with the least amount of thickness runout, and a sizing setup that helps to keep the case straighter than conventional one piece dies, with expander balls can.
 
nilescoyote said:
.......The loads made with lake city brass show the most run out. If I neck turn these will it improve the results. What is the best way to reduce run out?
Click to expand...

I have never neck turned brass, so can't answer that.

But, I am anal about concentricity, having only found out about the importance of it not too long ago in my National Match AR15. (.....at least if you are seeking top accuracy anyway. I assume that you are.) I have THREE GAGES to check concentricity, and can tell you that the 223 Federal Lake City brass is inferior to Remington......and the Remington ain't nothing to brag about! I simply sort my once fired Remington brass into two batches....one is "target" and goes into my plastic ammo box....the other batch for "defense" cartridges gets placed into a bag for bore fouling or for SHTF emergencies. I still do a final check and seperate the best of my finished "Target Loads" placing them in labeled rows according to how concentric they are. Generally anything that is inconcentric by 6 thousandths or less on the Sinclair Gage is premium target reloads. (ie; -6 thousandths indicated on the Sinclair gage is actually equal to 3 thousandths inconcentricity, since the case is rotated twice on it's axis) Those rounds are the cartridges saved for the most serious target work.


I have set up one Sinclair gage to measure just the empty case at its neck. If the case is satisfactory on that gage, I then place it in my Redding dial gage to measures just the thickness and uniformity of the case neck. If the case neck thickness is uniform, I then load and complete the cartridge. (after all the other steps of deburring, uniforming, trimming, etc) The 2nd Sinclair gage I have on duty is reserved just to measure the completed cartridge. The probe of this Sinclair gage rests on the bullet to check the final concentricity of the loaded cartridge.

I have found that Wilson seater dies will help to eliminate some inconcentricty issues. They seem to load the bullet straighter into the case then the standard 7/8" screw in dies. Not always so, but more of the time anyway.
 
"Generally anything that is inconcentric by 6 thousandths or less on the Sinclair Gage is premium target reloads. (ie; -6 thousandths indicated on the Sinclair gage is actually equal to 3 thousandths inconcentricity, since the case is rotated twice on it's axis) Those rounds are the cartridges saved for the most serious target work."

That sounds great, but can you explain why. Im not sure I understand why .006 = .003
If that is the case it makes me feel a lot better about my results. I knew the factory federal match ammo is good stuff and my reloads always seemed to do just as good if not a little better.
 
You would get a true reading of inconcentricity if the tool was built so it operated with a spindle holding and supporting the case through the neck. In that manner when you rotated the case it would be giving you measurements from off of the center axis. But being this tool supports the case by it being layed on its side and rotated on its side, the inconcentricity readings are actually doubled.

For an example which is much easier to visualize: Just imagine a chicken being placed in a rotisserie bar-b-que. When you run the spike-bar up through the middle of the chicken, it rotates over the fire fairly evenly. Now imagine if you just placed the chicken against the spike bar and tied it to the bar......it would spin very unevenly and very eliptically...making much larger circles.

Now you get it?

It's really not a problem to simply just half the readings you get. You will get used to knowing real quick which numbers are acceptable to you, and which readings aren't.
 
Chasing the dog

It could be your sizing die.

It could be your seating die.

It could be the brass.

It could be your press operation. (this must be a very smooth operation)

You really can get .002 or less with a .308. I demand it even with magnum brass.

I suggest you neck size with a Lee Collet die and seat with a Redding Benchrest seater die.

Recheck your operation. It takes a special touch.

Try some Lapua brass.
 
"In that manner when you rotated the case it would be giving you measurements from off of the center axis. But being this tool supports the case by it being layed on its side and rotated on its side, the inconcentricity readings are actually doubled."

Thanks, I knew that, but had forgotten. :)
 
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