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Help me determine what is causing my runout!

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  #8  
Unread 08-15-2009, 05:34 PM
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Re: Help me determine what is causing my runout!

Quote:
Originally Posted by Mikecr View Post
I don't agree with generalizing TIR-vs-R(cutting TIR in half) because your runout cause would first have to be determind before going there. For example, if your runout is caused by big variance in thickness, this will be indicated regardless of centerline conditions....
Unless I'm misunderstanding you, I'm confused. If you load a bullet .001" off the centerline of the cartridge case, you will measure .002" TIR. How could TIR and R not be related in a 2-1 relationship?

Unless you are talking about a neck that is crooked, then you should get vastly different TIR close to the neck and closer to the point.

AJ
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  #9  
Unread 08-15-2009, 05:42 PM
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Re: Help me determine what is causing my runout!

"..if your runout is caused by big variance in thickness, this will be indicated regardless of centerline conditions. And in this case, your runout would be exactly as indicated(provided that is your only contributer)."

If I correctly interprete your meaning, you are suggesting a potential for the neck ID to be exactly paralllel to the OD but off-set by what ever neck thickness variation that exists?

IF I do understand you correctly - and I may not - I don't agree with your perceived view of gaged TIR vs. actual run-out. The high side will read one level of error away from the true center line. A reading on the other side will read the same off-set but in the opposite direction. So, no matter the source of error, the indicated reading will effectively be twice the amount of actual run-out. That's just the way TIR works, regardless of the source cause of the error. (And a tip of the hat to AJ)

I'm told that many non-machinest's have some difficulty grasping the difference between run-out and TIR and how either is measured. (I'm NOT a machinist but I've had a good deal of hands-on lathe training from someone who is.)


"I also do not follow the collet die as a runout reducer idea. I just don't see how it would. What I see, is that it would contribute less towards additional runout."

Again, if I understand, it's hard to differentuate between not adding runout vs. correcting it. To some slight degree, the Lee collet die does both.

First, unlike a conventional small sizer button dragged through the neck, the Lee collet die cannot ADD any "bend" to a neck since the neck is squeezed hard against the straight, centerally mounted and firmly held mandrel. That's good, and it's unique to that die.

Second, if the inner case neck was originally formed with some anglular difference to the outside, the fact that the inside is forced so hard to the mandrel there will be some amount of straightening force applied. Including springback, there are too many variables in that for anyone to project just how much such a straightening would remain after the sizing pressure is removed but it sure can't get worse and it MAY be improved.

Last edited by boomtube; 08-15-2009 at 06:12 PM.
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  #10  
Unread 08-15-2009, 10:17 PM
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Re: Help me determine what is causing my runout!

All I'm saying is the runout may not be bent necks. Or necks off center. It could be both.. Or the case bodies can form into bananas(because of springback variance, due to thickness variance), throwing everything out.
There could be a combination of these things among others adding and subtracting in ways that don't just go up and down.
This isn't lathe turned stock, it's pressure formed.

For example, an angle might counteract an offset, or add to it. Let's say one or the other is significant. Until it's specifically measured, you couldn't really generalize about it. You can't just divide runout in half, because you could actually have more than that, it's just being counteracted by the other contributor.
You don't run into this often in machining, because only one parameter is being changed at a time. Step by step by step.
And identifying runout is similar in that you go backwards through the steps.

Now you could have a die issue, shellholder, or more common press alignment issues. The seater plug might be a contributor.. Good things to checkout.
But the base of all runout, even with all else perfect, is case thickness variance. It runs full length of the case. With this, runout will occur and grow with each firing, and with each contact with any die.
The devil here is springback, and if your not considering what's happening in that regard you might convince yourself of a die issue that isn't. The die is just releasing an inconsistent tension, and there is nothing I know of that can fix it. There are only things done to reduce the rate of runout growth(like neck turning & minimal sizing).

The fella starting this discussion mentioned runout before dies even touched the brass. This is significant in that it's independent of what has been discussed so far, unless he FL sized before fire-forming. I think he should go back to that. Fix that first.
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  #11  
Unread 08-16-2009, 01:20 AM
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Re: Help me determine what is causing my runout!

Yes the runout numbers I posted were what I was reading on the gauge. So TIR would be half that. Runout on cases right out of the chamber was almost nothing as would be expected.

I am using the standard Sinclair gauge, the roller bearing type.

Yes the cases were inside neck chamfered.

Yes I am the spring clip to hold the shell holder on the press. I will take it off next time and see if the numbers improve.

I am seating Sierra Match Kings. I would expect the .308 Redding Comp seating die stem to accomadate those quite well. I will take the die apart to see if there is debris in it or something else ammis.

I am the only person that I know that reloads so I cant try these on another press.

I always rotate the case and seat in several steps, always go easy on the handle to let things line up.

I am using a Lee Classic cast single stage. Is there a way for the average joe to measure press alignment issues?
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  #12  
Unread 08-16-2009, 08:57 AM
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Re: Help me determine what is causing my runout!

Quote:
Originally Posted by dmproske View Post
Yes the runout numbers I posted were what I was reading on the gauge. So TIR would be half that. Runout on cases right out of the chamber was almost nothing as would be expected.

I am using the standard Sinclair gauge, the roller bearing type.

Yes the cases were inside neck chamfered.

Yes I am the spring clip to hold the shell holder on the press. I will take it off next time and see if the numbers improve.

I am seating Sierra Match Kings. I would expect the .308 Redding Comp seating die stem to accomadate those quite well. I will take the die apart to see if there is debris in it or something else ammis.

I am the only person that I know that reloads so I cant try these on another press.

I always rotate the case and seat in several steps, always go easy on the handle to let things line up.

I am using a Lee Classic cast single stage. Is there a way for the average joe to measure press alignment issues?
Press alignment is tough to measure and is unlikely to be the cause. A shade tree mechanic method of seeing if the threads on the top are straight with the ram is as follows.

Put a die in the press and raise the ram, screw the die in and see if the bottom is square to the shellholder, if you screw it in just enough to let a very small gap, you'll be able to tell if its pretty square. Some of the cheap loack nuts will not lock the die in as square as others, so be aware of that as you lock the die in.

AJ
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  #13  
Unread 08-16-2009, 09:47 AM
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Re: Help me determine what is causing my runout!

In addition to all the other things try removing the spring from the inside of the die. I've found that the spring pressure can sometimes start the bullet before the case has risen high enough to be aligned by the die. Cliff
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  #14  
Unread 08-16-2009, 05:24 PM
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Re: Help me determine what is causing my runout!

"... base of all runout, even with all else perfect, is case thickness variance. It runs full length of the case. With this, runout will occur and grow with each firing, and with each contact with any die.
The devil here is springback, and if your not considering what's happening in that regard you might convince yourself of a die issue that isn't."


Okay, I see your point. Disagree with how it can be measured but your point of bad brass is well taken. I do sorta have a solution for those cases; I toss any that don't respond to my normal treatments!

After a couple of my "select-load-fire-reload-measure-toss the losers" cycles, the remaining brass is very good. (Wish I could shoot as good as my twice prepped brass is!)
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