Redding Comp seater runout?

[elmerdeer]

I have a RCBS Rockchucker supreme press and my runout on my 7mag is very good between .0005-002' I use lee collet necksizer and a Redding comp seater with nosler brass and 160grs accubonds. So now my problem, I also have the exact same setup for my 280AI using the same dies and brass, and the bullets are 140 accubonds, so why do I get runout of 0035'-009' out of my setup for the 280 AI? I have tried using an O-ring under the seater and it got a little better around 003' to 005' but that is not what I like. I am also waiting for my gunsmith to ream my Forster comp seater with the reamer used for my chamber and then I can compare if it gets better. But aside from that why is the 7mag get much less runout than my 280AI?
Thanks
Elmer

 

[fdshuster]

Elmer: By all means check the seater stem depth as suggested, but over many years I continually find that most runout is caused by the quality, or lack thereof, the brass. With the second loading and firing of new brass, now twice fired), any cases that continue to have loaded r/o of more than .003' are marked and kept for 'limited' use. With high quality brass, like Lapua, very few, if any will have the problem. 'Cheaper' brass, yes, could be as many as 10 or 12 out of 20. So, the question is: Why do some of the brass, from the same lot) have near zero r/o, and others from the same lot many? In my opinion, the r/o brass is defective at least to enough of a degree to cause the problem. Believe me, I've been beating myself up on this issue for many, many years.

 

[elmerdeer]

Hi,

Is the seater stem drilled out deep enough? Is the seater stem not cracked?

Good luck,
Bollocks

Yes the stem is good, and it is not cracked.
And I will measure the cases tommorrow after my range session, and they will have been fired a second time so I will see if my brass comes out straight from my chamber.
Thanks
Elmer

 

[fdshuster]

Elmer: You may want to consider trying to isolate the problem one step at a time. Take a fired case,, or several), check neck runout after firing. Full length size without the expander button/de-cap rod, check runout. Full length size again with the expander button/de-cap rod, check runout. If it's not a defective piece of brass, this is where I usually find the first indication of more runout than 'normal', and one of the reasons I use the Full length neck bushing dies, almost exclusively. Just a suggestion- costs nothing to try.

 

[Mikem]

Frank is correct, in that the brass has a lot to do with neck runout.
Try this, when you check a case neck for runout, take a fine point sharpie permanent marker and put a small mark on the low side of the case mouth, load and shoot it, then recheck it for runout, and you should find vary little runout. Then re size the neck, and reload the round, and check it again. In about 95% of all cases, there runout low side, will always be in the same spot as you marked. And this can only be due to the factory annealing process of the brass. Unless you always index you cases in your dies, and most dont.
Its easy to correct a case with runout, buy taking an unsized case and slip it down over the bullet, and push lightly in the direction of your mark, and the brass will pop back straight, most of the time.
I have spent many hrs studying this problem, and this is what I came up with, short of reannealing the brass often.
Mike.