Determining Seating Depth - Bullet Wear

[Beau]

I was using a Sinclair Hex Nut to determine bullet seating depth. I noticed that the nut wears on the test bullet giving a progressively shorter reading until it stabilizes about 4 thou less.
My question is which reading is most correct for seating depth, the first reading or the stabilized reading?

Also, when I set the seating die up, should I use the original, worn bullet or a fresh one?

 

[bobm]

Use light pressure when measuring with calipers. Go with your first reading. Tip: break any sharp edges on the tool holes where it makes bullet contact. Tool bite into the softer bullet jacket combined with too much caliper pressure will change measurements. Measure a few bullets with the tool as shown, they should be close to the same dimension. Use a fresh bullet for final depth setting of your die. I made that tool from a SS nut.