Attached is a picture of my Whitworth Hexagonal Mould.
 
Weight of mould with handle and cut off plate is 12 ounces (343 grammes)
Base plug and handle is 4 ounces (114 grammes) and push out rod for the bullet is 3.3 ounces (95 grammes).
 
Inscription reads WHITWORTH / MANCHESTER / 112  and on the other side  
530.G.    C .470  /  F .440
 
These last refer the measurements across the corners and flats.
 
This mould is part of a cased set from 1859.
 
No mould serial number ever agrees with rifle serial numbers.

Surviving invoices for Whitworths detail each accessory supplied item by item including the case itself.  This suggests that if anyone wished to buy a mould by itself then - no problemo ! (other than having to pay for it).  The completely separate numbering sequence for moulds confirms this.
I, too, have heard that the bullets were machined from extruded hexagonal wire but, on balance, I favour the the production by Anderson's Bullet Machines as being more likely.  The absence of original factory records makes life very difficult.
When one looks at the mass production by automatic lathes in the period of boxwood plugs for the cavities of P/53 bullets, it is easy to imagine that such facilities as bullet turning could have been done.