Apologies if this is a very well worn topic, but a short while ago I was interested in understanding the significance of the number "125" on an old bullet mould, and was told it was the "bore". I had only heard of this term being used in connection with shot guns, which didn't seem to help. I learnt that the bore was actually the NUMBER OF BALLS PER POUND OF PURE LEAD that could be made. This meant that my mould would make ball 125 of which, would weigh a pound or 454 grams. So far so good BUT what size, or calibre would these be? Finding the density of lead, and knowing how to calculate the volume of a ball or sphere (as any school-boy should) I was able to find that my mould would cast ball of calibre 0.33 inch. Interesting - BUT I actually needed 0.32, which by reverse calculation gave a bore of 140.

Having worked this out, I learnt how to use a spreadsheet programme on my computer and have made a table from 1 to 200 bore, and if anyone would like a copy, please PM me. Also, if I have made any mistakes, I should like to have them pointed out too. I still don't understand what "12 bore" really means as applied to shot guns, and am sure someone could tell me.

plumbgun