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

 

[boomtube]

"why is the 7mag get much less runout than my 280AI?"

Better brass. You probably need to turn the 280 necks a bit. No seater can seat bullets straight if the interior of the necks are non-concentric. If I'm right, working on the dies won't accomplish a thing.

 

[nheninge]

What type of runout? Case runout? Bullet Runout? Where are you taking your measurements? Difference in brass? Rotating cases during seating?

I suggest you go back a few steps and test for runout during the whole process to find out exactly where it develops. You may be able to find a certain step that gives you the most runout and work to solve exactly that problem.

Or maybe you are "stacking tolerances". A little runout here and a little there leaves you with a trainwreck at the end.

Boomtube, are you talking about inside neck reaming, or outside neck turning or both?

I agree working on the dies MAY help but MAY not the source of the problem

 

[elmerdeer]

What type of runout? Case runout? Bullet Runout? Where are you taking your measurements? Difference in brass? Rotating cases during seating?

I suggest you go back a few steps and test for runout during the whole process to find out exactly where it develops. You may be able to find a certain step that gives you the most runout and work to solve exactly that problem.

Or maybe you are "stacking tolerances". A little runout here and a little there leaves you with a trainwreck at the end.

Boomtube, are you talking about inside neck reaming, or outside neck turning or both?

I agree working on the dies MAY help but MAY not the source of the problem

Bullet runout between 003" to 009" average 005", Case runout 001" to 0035" average 0025" all these are from once fired Nosler 280 AI brass, I will check runout after the range this fri ti see how they are coming out of my chamber, will post numbers.
Thanks
Elmer

 

[Winchester 69]

Variation.

If you're using tools with wide production variances to save money and hope that it won't come to play, the more you play, the more you lose.

If you're using considerably more pressure sizing the AI loads, I'd look at the press. On the other hand, what does the run-out look like on the fired AI cases?

 

[KQguy]

I was having the same problems as you,I had good runout just prior to seating the bullet.I am using a Forster comp. seating die.After experimenting,it just came down to technique,I would try different seating techniques,and write down the results to see which one worked the best.I would seat them with one steady pull,seat a little then rotate 90 degrees,then seat the rest of the way,seat a little,and keep rotating 180 degrees each time,until it was fully seated.I would try several approaches,loading 3 rounds at a time,then write down the average runout from each technique and see which way gave me the best average runout.With my equipment,rotating 90 degrees at a time,until fully seated gave me the best results,about .002'' runout on average.I also started finding the high spot on my runout,and gently applying a little pressure on it with my thumb and by doing that,I can pretty much get my runout down to .0005''.

 

[elmerdeer]

I was having the same problems as you,I had good runout just prior to seating the bullet.I am using a Forster comp. seating die.After experimenting,it just came down to technique,I would try different seating techniques,and write down the results to see which one worked the best.I would seat them with one steady pull,seat a little then rotate 90 degrees,then seat the rest of the way,seat a little,and keep rotating 180 degrees each time,until it was fully seated.I would try several approaches,loading 3 rounds at a time,then write down the average runout from each technique and see which way gave me the best average runout.With my equipment,rotating 90 degrees at a time,until fully seated gave me the best results,about .002'' runout on average.I also started finding the high spot on my runout,and gently applying a little pressure on it with my thumb and by doing that,I can pretty much get my runout down to .0005''.

But when applying pressure on the high spot and fixing the runout does affect neck tension differently from Rnd to Rnd, and wont that affect accuracy of the rnds in any way just curious in your results after having done that?
Thanks
Elmer

 

[KQguy]

My smith actually got me started on this way,he's got me using a standard FL resizing die,with the expander ball ground down,so it is not touching the neck.This gives me quite a bit of neck tension(.008").He's the one that told me to tweak the bullet runout,by applying a little pressure to the high spot.By taking his advise,and using his rifle,I am getting 1/2 moa accuracy to 500yds.It will shoot better than that,but that's all my shooting skills will allow for now.I am sure some people will disagree with this approach,but it is working great for me.

 

[boomtube]

"Boomtube, are you talking about inside neck reaming, or outside neck turning or both?"

Something of a quandry isn't it? What to do, what to do...

Mostly, I avoid reaming because it only reduces neck thickness and leaves any non-concentric inside and outside diferences intact.

Turning (usually) makes the inside and outside concentric BUT, if the mandrel isn't really tight, an off-axis center line (internal vs external cylinder dimensions) remains to some degree. What to do? What I do is neck turn it and if that don't fix the runout, I toss that piece of brass OR mark it and keep it for foulers, etc., if it isn't too bad.

For my factory chambers I never turn more than maybe 75% of the neck circumference, mostly just to clean up the worst of the thickness variation and still have as thick a neck as practical.

When I reform cases and end up with really thick necks, such as making .22-250 from .30-06, I turn to just under MY chamber's neck diameter, not just to max book neck diameter. That gives me near perfect necks but limits its use to myself. But, it's MY ammo and I make it FIT MY rifle, it's not made to fit every SAAMI rifle the factories ever made with that cartridge!

Point is, neck turning can HELP make straight necks for any case but it isin't magic so it can't cure them all.

I don't think reaming, alone, helps accuracy at all but it does insure safety from too thick necks.