I have tinkered around with the problem you are having for years, if you are using a RCBS FL die and can really get .003 runout consistently then stick with it but chuck your standard seater in the trash and get a Redding or a Forster (competition -BR )seater. they DO NOT straighten out a case but they dont make it worse,if you can size a case with .003 runout it can seat your bullet with .003 runout, a standard seater might seat one bullet at .003 and the next at .010 runout (especially RCBS) while you are at it just get a bushing die for sizing and live happily ever after at .001-.002
Thanks loads for your advice. I do indeed get the odd one that is pretty straight and the next one will be 10/1000 out. I will try your suggestions and will probably start with a good Forester in-line seater.
Just so you know, even the "bad" ones will average under 5/8 out of my bone stock rifle, which, I should add, is a Ruger #1 B, not exactly a benchrest rifle! As one friend put it, "if the damn things shoot OK, what the hell are you worrying about!?" I'd say he's right!
Over the years I've come to believe strongly that it is a match of the load to a good barrel and finding the right harmonics that "makes the load". And, yes, I do believe the barrel can and does straighten out the bullet. I've seen people report here on forums that for every .001" runnout over .003" you will see 1/4 moa loss in accuracy.
Obviously your gun and my gun shoot that theory all to heck.
If you're benchresting at 600+ yds and your match is won or lost by 10ths of an inch I'd say go crazy over runnout. I've owned a gauge for about 4 yrs now and I do check my dies and fine tune them for good runnout just to eliminate a variable. BUT, my experience in my hunting rifles tells me not to take it so seriously anymore. NO matter whether you use normal full length dies, collet dies, or bushing dies you will always have an array of runnout from a batch of reloads. It's pretty easy for anyone to check for themselves if it really matters in THEIR gun with THEIR load. In general I believe most hunters will find the differences basically meaningless.
If anyone cares to read it....below is a copy of what I normally post to questions like this and it's worked for alot of people.
My $.02 worth---ALL dies with expander balls need tuning. Think about it...a piece of typing paper is .003" thick--what are the odds that the expander is not PERFECTLY centered in a die??? Pretty good I'd say. Pull the expander stem out of the die (and now is a good time to clean the inside of the die). Run about 5 brass into the die and see if they come out concentric. If they do (and usually they will) you now have to try and get that stem centered on re-assembly. A great way that helps is to put a piece of very concentric brass up into the die to hold the stem in place as you tighten it down. Sometimes this takes 2 people unless you have 3 or 4 hands. AFter reassembly try sizing some brass and check runnout. If not good then do very small turns of the expander stem--probably 1/32 of a turn at a time. Resize some brass and repeat the small turns. At some point I can almost guarantee that you will get GREAT RUNNOUT CONSISTANTLY. (Somehow, someway the expander spindle will hit almost perfect centering in the die body) I have many dies that consistantly make less than .002" runnout after sizing with most of the brass at .001" and less. I own, hornady, redding, forester, rcbs, and lee dies. ALL OF THEM HAVE BEEN TUNED and most make fantastic ammo and all make good ammo!! I have never ever got a set of dies from any factory that made as good of ammo as those that I have done this simple work with.
most of what you say has some truth to it but I was talking about the seaters, if you tinker around with a sizing die you can probably get it to work O.K. if you are not too picky, but the point I was getting at is that standard seaters are junk and DO induce additional runout,if you get a good seater it will keep your runout the same as when you sized it.
Brian--non of my post was pointed at you at all. AND I know what you mean that a poor fit of the seater stem can cause trouble with certain profiles of bullets. I've got some of the forester dies and love em--they "feel" like quality. Hornady's on the other hand "feel" like a beer can but wouldn't you know it.........I've been able to get fantastic performance out of most my Hornady's and no longer spend the money on the Foresters. I've seen posts where guys have had nightmares with Hornady. It's always different strokes for different folks---the great thing is usually any factory maker stands behind their dies if you just send them in. I don't really understand how anyone makes the quality we see for $20-25 in standard dies!!!! $20 just doesn't seem to buy "anything" any more let alone something with some quality steel and machining.
Since I started using the Lee collet neck dies and Redding Competition seaters I have pretty much eliminated any and all runout issues I was previously having. My results at the range have been more consistent (as in better groups on average) as a result.