Cast Lead Thread ?

[Moa Hunter]

Today I did it again with weight sorted bullets

First three bullets went into 15mm at 100m and then the fourth went 100mm low
That has me a bit confused until I went back to the loading bench ( 5m from my shooting bench ) and realised one bullet was missing from a completely different pile of 38 bullets
So that was my flyer

But now I have stripped the block and am making a new firing pin because the one in it was made by Bubba

Attachment 206034

Great group those first three. How many shots would it take on average before fouling / leading makes accuracy drop off ?