Run out ?

[RAVEN]

Reporting in from SA
No Comment

[AlanF]

I have a question about this runout you blokes are talking about.
Is it the "angle" that the bullet is sitting in the case, compared to the line of the bore? That is, the tip runs out, but the base does not.
Or, is it the "offset" of a bore aligned bullet, to the bore. That is, both tip and base run out in unison.
The latter may be caused by a case neck with differing thickness on each side?
A bullet that has runout of .010 or more, would surely align itself to the tolererances of the chamber? I would think it would come back to the tolererance or difference between the bullet diameter and the throat diameter, assuming that a pre-fired case is a snug fit in the chamber.
I can't see that diameter difference being .010, but just what it really is, I don't know.
I agree with Pete that the correction should be in the loading dies.
Howard.

With mine its mainly the first one, and is usually caused by the neck alignment not being parallel with the bore. Seating can help to correct it, particularly when bullets are seated only part way into the neck. With my dies the root cause has been bumping the shoulder - it appears that the brass doesn't always squeeze in uniformly round the shoulder, resulting in one side of the neck being pushed out more than the other, and the neck bushing probably tilts a little in sympathy. I overcome it to some extent by FL sizing 3 times in rapid succession at 120 degree rotation intervals.

[Bindi2]

Don't know how any of you buggers can see with your heads where they are.

Head lights an open eyes.

[pjifl]

While quoting 'runout' in linear measure I am thinking of angular misalignment. Technically it is wrong but relates more easily to the simplest way to measure it.

Lateral misalignment is usually minuscule. Certainly after neck turning and even with most commercial necks.

I feel the most convenient way to measure this 'runout' is to

1/ Insert the bullet point into a small funnel shaped cavity made with a very large centre drill - with the small straight pilot hole drilled further so there is no chance of the bullet tip bottoming. This makes for quick and convenient insertion. Best made of a soft metal like Al.

2/ Rest base of bullet just in front of the extraction groove in a V

3/ Measure runout on bullet where it is exposed just past the case neck, while turning it and pressing down and forward gently with the fingers.

Other runout gauges may use a slightly different arrangement but still measure a similar parameter. The first runout gauge I built uses this system and subsequent designs also do because I think it is the simplest for a portable one to use. It does not have to be very elaborate nor very expensive.

This is less sensitive with smaller, shorter bullets and I have seem somewhere reference to acceptable standards for different sizes.

I think the best use of runout measuring is by regular sampling. If there is a significant change there must be a reason and hopefully you catch the problem before it becomes an issue.

Peter Smith.