Brass Runout Issue

[Jayhawker]

I have found an issue with runout after full-length sizing new Lapua 6 BR brass. Out of the box, the brass gives an average of .0005" runout. Once lubed and sized with my Redding die another check shows .007" runout. When this is repeated, the measurement may drop somewhat but can change each time I repeat the sizing. This is about the same with my Redding full length/bushing die only to a lesser degree. Redding wants to look at the dies so I shipped them off the New York. I have a hard time believing that two, relatively new dies have "gone bad", however.

On the other hand, I started looking over my Rockchucker press which isn't so new. There is not much, but a definite back and forth play especially when the ram is at the top of the stroke. In addition, I noticed that my shell holder does not snap in with some pressure like a friend's does but more or less glides in with minimal resistance.

I'm certainly leaning towards the press as the problem. Has anyone had any recent experience with RCBS? Do they replace or rebuild if indeed they think this is a problem? From what I've seen the Rockchucker, for what it is, is the go-to press for many reloaders but are there better ones that other readers would recommend?

Thanks and Merry Christmas.

 

[Zia Hunter]

A couple of things you may want to check. If you are using an expander plug in your die that could very well be the source of your problem. Resize a piece of brass without the expander and check for runout. If the case is concentric, it is most likely caused by the expander. Redding makes a carbide expander ball ball that floats on the stem and generally helps with the issue. I install O-rings between the die body and the decapping stem lock ring which allows the stem to float. Insufficient lubrication of the inside of the necks could also cause the problem.

If the case is not concentric after FL sizing without the expander, the problem could possibly be the die or die misalignment in the press. Clean the top of the press surface to make sure the lock ring mates square on the press and check the lock ring as well for defects. There have been a number of threads that discuss using an O-ring between the lock ring on the die and press and you may want to reference those. The probability of the die being bad is pretty remote but if so Redding will replace it.

If you are neck sizing with a bushing you probably won't need to use an expander. The bushing size should be .005 or less the neck dimension of the fired case. If it is greater, the force of the bushing on the neck can result in runout.

I have a Rockchucker press that I bought nearly 40 years ago and the linkage was getting sloppy giving me headaches. Replaced it with a COAX and wish I had done so years ago.

 

[Jayhawker]

Zia Hunter:

Thank you very much for your suggestions. You may be interested to know that the RCBS tech I emailed with a description of the problem, states that only the dies could cause runout and his mail was accompanied by an explanation of sorts.

I normally do not use the expander plug on either my full length or bushing/full length dies but did this time to see if it helped-it didn't change anything. The only reason I was using the full length die in the first place was because it was new brass and, as suggested by German Salazar, a full length die will not leave a "donut" at the bottom of the neck that gets turned off.

I'd like to try the o-rings but my dies are spending Christmas at the Redding company. I have to agree with you, the odds of having the dies out of alignment are pretty remote and at the same time, I can't see how a press with play in the ram wouldn't be a problem.

 

[BoydAllen]

If I were diagnosing this problem up close, I would proceed as follows. First I would measure the runout of a fired case, measure it's shoulder diameter, and the diameter where it was the largest, somewhere above the extractor groove. Then, with the die set to produce a MEASURED .001 shoulder bump (assuming that the case had been fired enough times, at a high enough pressure, to need bumping) I would size the case, without a bushing in the die, and compare the runout to what it was before sizing. I would also remeasure the diameters that I had measured before sizing. If you will do this, and report your results, perhaps we can proceed from there in an organized manner. While you are at it, check your bushing for runout between its ID and OD and several spots, with a neck mic., and make sure that the bushing cavity in the die is clean. as well as the shell holder slot in the top of the ram, and the shell holder groove that fits the rim of the case. Loosness at the top of the stroke is not the fault that many think it is. As a matter of fact, one of the better benchrest shooters in Texas cuts his rams down slightly in diameter to let cases self align with the die better. Another thing to try is to use an O ring under the die lock ring, with just enough compression on it to keep the die from turning, no more. Lee lock rings have this built in. Again, the idea is to leave the O ring minimally compressed so that the die will align to the press threads when forced up or down, during use. As long as it does not rotate, its setting is secure.

 

[bigedp51]

In the Speer reloading manual #9 dated 1974 there is a very good article that has been a big help over the 45 years I have been reloading.

"Modern Benchrest Reloading Techniques"

1. Shell holder must fit correctly and not bind the cases when rotated in the shell holder.

2. Loosen and raise the lockring on your die and place a lubed cartridge case in the shell holder, raise the ram and allow the lubed case to center the die in the press threads and then tighten the lockring.

NOTE: When all else fails and the above didn't work get a Lee Collet die and check your runout.
(don't hate yourself if the runout gets better after spending all that money on more expensive dies)

 

[Jayhawker]

Thanks for the additional suggestions however, as I mentioned, my dies and shell holders are on their way to Redding for checking. After that, depending on what they say, I can make those checks.