Re: Help, concentricity problems.
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I've been reloading (clean, deprime, prime, powder seat) for 30 years. All my rifles will shoot sub-MOA.
My problem is that until recently, I just worked up a load, reloaded (sorted brass by weight), weighed each charge and called it good.
Since I ordered a 338AM from Kirby, I decided I needed to be able to measure things like bearing surface length on my bullets (so I got some stoney points gauges), Concentricity (so I bought a Sinclair gauge) etc.
Well, I grabbed my box of Norma 7RM brass (mostly once fired, some still virgin, some loaded) and started checking the concentricity.
WHOA!! measured just in front of the neck, the loaded rounds run from .0015 - .008 runout. The once fired measured on the neck runout .002-005" and the new virgin cases run .002-.004" runout.
I immediately measured some of my .243 winchester rounds same type of resolts, then the 7mm-08 same thing, then some factory Remington 7RM, it measured .002-.006" runout
On the .243, I use Pacific neck size dies, on the 7RM I use Forster Neck die, on the 7mm-08 I use RCBS full length.
I polished the expander button on the 7RM Forster neck die, and resized some of the brass; no real change before-after on case neck runout sometimes .001 better sometime .001 worse.
I'm not setup to measure neck thickness.
Since its pretty much the same on 3 different calibers and the factory ammo, do I have a problem? The runout numbers above are extreme spread on the dial indicator. I read that .002" was an allowable limit for runout with bench guns etc. These are all factory chambers with nothing done to the brass but trim/chamfer flash hole debur.
I'm using the same Rock Chucker single stage press I've been using for 30 years.
I now understand the saying "ignorance is bliss".
Any ideas are appreciated.
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Well, I'm happy now. My concentricity problems were solved with a "get back to basics" approach.
I read the Zediker book "Handloading for Competition" and took all his advice with regard to setting up my dies etc.
Here is the step by step I followed to resolve my 7RM concentricity problems.
I purchased a neck thickness mic from sinclair, as well as the mandrels for using my sinclair neck turner for the 7mm.
1) Removed the shellholder spring from the presses.
2) Polished the expander button on my FL size die and cleaned the die.
3) 'Tuned' the decapper assembly to center in the FL die.
4) Measured everything on my once fired Norma brass (head to shoulder, neck thickness etc.) and wrote it all down.
5) Sized all the brass, noting its orientation in the die.
6) Neck turned all the brass to .0145" thickness. This brass was very consistent. Typically only .001" or less variance. .0145" just barely cleaned most of it back to a variance of nil.
7) Sized all the brass again, orienting the brass 180degrees different than the first time. (checked Runout, all but 2 were under .001" runout measured halfway up case neck)
8) Primed, Powder
9) Seated using an old RCBS Mic seating die to within .002" of the lands. This die does not guide the case with a spring bushing. Runouts increased at this step by around .0008". This resulted in an average runout measured on the bullet of .001505" for the 20 rounds I loaded.
I believe I can improve the seating die runout problem by purchasing a good Forster seating die with the sliding case support.
I also believe my old RCBS shellholder is not 100% true, it was leaving flats inside the rims of the cases. So I think I'll get a 'competition' shellholder and see if that helps.
One additional thing that the book recommended, was to use Imperial sizing wax. I agree with Zediker, that this wax does a more consistent job than anything I have used before (I was using the spray on lubricant).
Thats it, the 20 cases I loaded are for a ladder test with the 162gr A-max and IMR4350.
I'll update this thread after I perform the test.
If some is good and more is better, then too much is just right.
My mind is a raging torrent, flooded with rivulets of thought, cascading into a waterfall of creative alternatives