GWS,
I took your data and averaged the changes in runout for all 5 rounds, then took the differences between each successive sizing step. The result, with mils meaning thousandths of an inch in this case, was:
Code:
No sizing Sizing 1 Sizing 2 Sizing 3 Sizing 4 Sizing 5
Step: 1 2 3 4 5 6
Avg. runout in mils: 5.0 3.7 2.7 1.825 1.7 1.0
Improvement in mils: — 1.300 — 1.000 — 0.875 — 0.125 — 0.700
Except for the small change between steps 4 and 5, there is a very steady logarithmic reduction of improvement with each sizing step, which you would expect because there is less improvement to make with each pass. There is no indication I can see that rotating the case did anything two additional unrotated sizing operations would not be expected to do.
Quote:
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Originally Posted by GWS
…Of course expander pulling got even easier with each successive sizing…
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That supports my burnishing theory. You are also burnishing the motor mica into the brass surface, reducing pull on the neck each time. The uneven neck thickness Bart referred to is also going to be a factor. You are probably nudging it a little more to the side with each pass, tending to line it up with the more axial neck position. The same thing happens when you lap a bore irregularity under a heavy-handed dovetail cut. The part of the bore that's out of line with the rest gets rubbed harder by the lap. In this case any part of the brass that isn't on-axis gets more burnishing pressure from the expander, which has the rest of the neck trying to keep it lined up.
Bart's point on the burr edge is another good one. I once seated then pulled a moly-coated bullet from a freshly trimmed and chamferred case and there was no remaining trace of the moly below where the bullet met the chamfer. I was scraped as clean as a whistle. Burnishing the wire edge off the case chamfer fixed that. I hadn't yet got the E-Z out idea from Bart at that time, so I just sharpened a dowel like a pencil and spun that against the case mouth with a drill. That worked, but needed constant resharpening, where the E-Z out is a permanent tool. But another thing I tried that worked was running the case mouth over the carbide expander in my sizing die a couple of times. Either way, that stopped scraping moly, so the drag was gone, too.
By the way, if you examine commercially loaded ammo closely, it's not uncommon to find a little scraped copper where the case mouth meets the bullet. Just keep an eye out for it. The cause is the same as with scraping moly.
Bart's also answered why you can't get below 0.001" runout. Take a steel straight edge and lay it along the side of each case and look at the cracks of light that appear where the wall isn't straight. Rotate the case and you will see these light cracks change size and position. Occasionally you find one that is uniform all around, but they are the exception. Most have some degree of unevenness, and that is what is meant by a "banana shaped case". It's one with side walls that aren't straight and bulge more on one side than another, putting a slight curve into it.
Lots of guys lap the way Bart described. You can cut a little faster and need less feel and technique to keep the cutting randomized with a commercial hone. You can use a
Flex Hone the right size. They can be had for
around $10-$12 from here. Call the maker for help picking out the best size and watch their videos on how these tools are used. If you buy from the company directly you pay MSRP, while the second source, when they have the size, is between half and three quarters of that price. You can slug the die neck to learn its size, or you can use a pin gauge or a small hole transfer gauge to track your progress.
John Feamster, writing in The Precision Shooting Reloading Guide, compared ammo off the standard RCBS sizing and seating die set to ammo off the RCBS Competition die set, and after seating 100 rounds with each, actually got somewhat better results from the standard set. He also compared 50 rounds seated with an RCBS standard seater on a Dillon 550B press to 50 seated with a Wilson seater die on an arbor press, and got better results with the standard RCBS die on the Dillon press. Things don't always work out as expected. And this book was published in 1995, so if the die design changed it may no longer be a valid result.
Feamster did use a rubber O-ring between the lock ring/nut and the press with the sizing dies to let them have a little wiggle room. The Lee lock rings do essentially the same thing if you don't make them dead tight. I've had mixed results experimenting with this and concluded I needed to lap the press and die threads smooth and use a little high pressure lube on them to get the full effect. STP works fine.
I've never tried mixing STP with Hoppe's, but I have mixed it with odorless mineral spirits and Kroil. Either thins it. They may trouble your spouse's olfactory senses less than #9, though they won't clean powder residue off as well. The mineral spirits are particularly slow to affect powder carbon and graphite.