Originally Posted by boomtube
"Especially cases coming out of large factory chambers with a bulge on one side and if that bulge sits on the gauge supports ."
I don't care how 'accurate' my runout is from a mechainst's point of view, what I want to see is no wiggle on that gage.
Given your recognition of how difficult it is to properly support a cartridge so the results are of runout rather than case inaccuracies drove me to make my own runout gage. Wanting to know the relitive angular displacement of the bullets led me to a system I've seen no where else.
The only machined surface on a case is the extraction groove. I have a 1/16" thick bit of sheet teflon with a "V" cut that the extractor cut drops into. A similar teflon V notch is adjusted to support the bullet just outside the case mouth. The dial indicator plunger is positioned as close to the meplat as possible but not where pointing irregularities could influnce the gage. Slowly turning each cartridge gives me consistant high and low readings at the same places, total indicated runout, over most of the bullet's exposed length and that's all I need.
That is an interesting idea and if it does what you need then it's a good idea.
It's a very complicated issue and as we are measuring loaded rounds they have been through sizing and seating dies that make changes to the brass.
What I do at the moment is use a V block to support the case in the middle away from the shoulder and base and rotate in that . It is far from perfect but it is cheap . What I do is indicate the neck first then the bullet and compare.
If the neck runs out then whatever I read on the bullet is also partly neck run out. If the neck is fine then whatever I read on the bullet is seating run out.
I am sure it is full of holes but it gives me an idea of how my sizer and seating dies are working . If I get more neck runout after neck sizing turned cases than I had just after firing then I get a new die or look at how I am sizing , cleaning , lubing , whatever .
I dumped expander ball type neck sizers in preference for Lee collet and bushing type dies and also full length dies in preference for body die . Also bought a few comp seater dies.
After that I saw straighter necks and less bullet run out but bad brass can screw you up some times .
My case necks are skim turned to do this but on other guns I don't neck turn so I don't bother testing bullet run out . I just tune to the best accuracy I can get and leave it at that.