I'm starting this thread because I'm having a problem properly measuring my boolits with a micrometer. In a nutshell I believe the micrometer is squeezing the boolits enough to spoof the measurement by half a thou or so.
Recently I beagled one of my molds and I cast some oversize boolits using 1:20 alloy. As cast they measured 460~462. Then I sent few through a Lee 459 resizing die. Imagine my surprise when they measured exactly 458! I thought that maybe it is grease that causes it. So I degrease the die with acetone. I lubricated the boolits only with s bit of wd40 and I run another one through the die. Again it measures 458.
Few words about me and my measurements. I have been a hobby machinist for almost a decade. I have various micrometers, calibration gages, a granite surface plate etc and I believe I know how to use them to measure things made of steel, aluminium, bronze etc. However, lead alloys are problematic.
99% of you that read so far probably thinks my Lee sizing die is undersized. I thought so too. Before I prepared everything to lap it bigger. I measured it with a bore gauge and it turns out it is exactly 459 thou! (maybe a tenth or two under, but no less).
So I tried to be very careful when measuring my boolits with the micrometer. Instead of turning the knob as usual until the clutch mechanism clicks I set the micrometer to 459 exactly and tried to move the boolits to pass through the measuring faces. I did manage to push it through with a little bit of noticeable drag. However, when set to 458.8 there is no way I can push it through. However if I measure it "normally" it measures 458.0. I also tried moving the boolits gently between measuring faces while moving the micrometer slowly from 459 to 458. It grabs at around 458.6 with enough force so I can't move it any more gently. However the clutch doesn't engage at this stage. The knob can be turned further half thou before it clicks...
It is quite a bit of a puzzle.
I was considering measuring it with a dial indicator on a stand on a surface plate (referencing off some gauge blocks), but those dial indicators feel like they apply quite a bit of force too. So that's not going to work to give me any certainty about the dimension.
Any ideas? What is your way to measure boolits? How do you avoid this problem?