Originally Posted By: 2-piper
In the article black powder was stated as used for "Provisional Proof".


Further down the article states:

"The Definitive proof takes place in another adjacent shed where the gun, minus stock work, is laid in a cradle and after being covered with a ballistic blanket, is fired by means of a lanyard into a sand bank at the far end of the shed. The proof cartridges are loaded on site with a carefully measured load of black powder and shot."

This was the part that really surprised me.