Help me with Runout!


Formerly 'TrevorBD'
Sep 23, 2020
Carlsbad New mexico
Alright so I have recently built a new rifle, it is a 300 Terminator that defensive edge chambered/barreled the action for me. It came with their custom dies which are Redding type S bushing dies. I have been measuring anywhere from .006” to.008” runout of a seated bullet after resizing the case, bumping shoulder back .0015”.

I have measured runout of the neck on a fired case (nonsized) and its near perfectly concentric, less than .001”. Resized the case, then measured again with a reading of .006” runout. Narrowing down my problem to the sizing.

The sizing die came with a sizing button in it and I had been using it. After researching and coming to the conclusion that sizing buttons are typically not great for very concentric sizing, I went by Redding’s recommendations by measuring the neck of a loaded round (.308”) and using a bushing .001” smaller in diameter. So I ordered a .307” and a .306”. I threw the .307” bushing in, lettering down, (left the shaft for the sizing button in the cap with the little locking ring that acts as a stop for the bushing) tightened the cap and backed it off a hair just like Redding says to. Measured a fired case, less than .001” runout out, then sized it, with the new bushing and no sizing button, and still got a new runout measurement of .006”.

I have tried many things-
Removed the snap ring for the shell holder and applied grease to it to allow it to float, floated the die itself with an o-ring, tried different shell holders, tried the other bushing, all with no help at all to my issue.

I am starting to point the finger at my press maybe? It is a RCBS rock chucker. Just wanted to see if anyone with more experience than myself can shed some light.


Well-Known Member
Sep 16, 2014
Northern Kentucky / Cincinnati
I wonder if your die might not be concentric?

Can you use a sharpie to index the case, size it, check for runout and mark the case where the runout is the worst ... then, turn the case 60 degrees or so in the shell holder, size again, check runout again and mark where the runout is worst ... if they are different spots and off by the same degree of rotation you put on the case in the shellholder, I'd be suspicious of the die

I've never heard of a press being the cause of such a thing but others here that know a lot more than I might be able to offer more on that theory ...


Well-Known Member
LRH Team Member
Nov 28, 2014
Wilsall, MT
nkyshooter nailed it. I would suspect the die long before the press. A normal RCBS shellholder would have enough float to accommodate .006 run out. Redding has great customer service so I am sure they will take care of you.


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