Calibre vs. bore

[plumbgun]

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

[DedIdick]

I still don't understand what "12 bore" really means as applied to shot guns, and am sure someone could tell me.

Shotgun gauges are easy......12 gauge (or Bore) = 12 balls from 1 lb of lead.
16 ga = 16 balls from the same lb of lead and 20ga gives 20 balls from a pound of lead, simples!

[Tantomurata]

I learnt that the bore was actually the NUMBER OF BALLS PER POUND OF PURE LEAD that could be made....I still don't understand what "12 bore" really means as applied to shot guns

You've answered your own question. 12 lead balls of 0.729" nominal diameter weigh 1Lb. Therefore 12 bore has a nominal bore diameter of 0.729"

Don't forget that where a patched ball is used, the ball diameter is less than the bore diameter to allow for the thickness of the patch.

[plumbgun]

That makes perfect sense-so long as the shot in a 12 bore shotgun cartridge are nearly 3/4" in diameter well 0.7+ inches anyway. Is that REALLY right??

[plumbgun]

So it's obviously nothing to do with the size of the shot!!

[Tantomurata]

That makes perfect sense-so long as the shot in a 12 bore shotgun cartridge are nearly 3/4" in diameter well 0.7+ inches anyway. Is that REALLY right??

So it's obviously nothing to do with the size of the shot!!

Nothing at all to do with shot size. It simply relates to how many lead balls of the internal barrel diameter (caliber) weight 1LB.

It just so happens that 12 lead balls of 0.729" diameter weigh 1Lb, therefore a gun with an internal barrel diameter of 0.729" is called a 12 bore.

Shot can be anything in size from 'dust' to a ball of bore diameter, although a ball of bore diameter would not normally be called shot. The term shot tends to be used for multiple projectiles that are smaller than the actual internal barrel diameter.

For a 12 bore cartridge gun, shot sizes are usually anything between No.9 shot and LG (0.36" diameter). Above LG it would be either a single round ball, (aka solid ball) or a single slug, possibly a pre-rifled design such as a Brenneke.

[DedIdick]

Obviously.

[plumbgun]

Obviously.

I suppose everything's obvious when you know the answer. as I said, I am new to this!

[DedIdick]

I suppose everything's obvious when you know the answer. as I said, I am new to this!

Obviously!

[plumbgun]

Ta mate