Mick B.
Your friend is very fortunate to have one of the original Rigby's.  There is a guy here in the states that set the 900 yd muzzle loader record this spring with an original that he traced back to one of the later Creedmoor matches that was held here.  I got to look at it and it is a beautiful rifle.  I think this one sold down under a few year ago.  Bob

Grisen
The rifle is a .45 muzzle loader.
MB
The loading information that came with Dougs rifle makes no mention of blow tubing but that doesn't mean they didn't do it.
For almost fifty years before I started shooting BP cartridge rifles I shot percussion and flintlock longrifles. On our range placing your mouth over the muzzle and blowing down the barrel was specifically forbidden for safety reasons, so I assume you meant using some sort of long tube put down the barrel with a flexible tube on one end perhaps. Almost everybody I saw both here and at Friendship wiped their muzzle loaders between shots. As for the use of false muzzles on the Rigby I will have to get back to Doug and ask him about that, perhaps I'm confused and what I saw was just a straight line bullet starter that slipped over the muzzle. As for the legality of using one, I'm uncertain if the rules and regulations in Australia at the time prohibited their use or not.
Mike.

metford in his instructions for using his long range muzzle loaders insisted that the shooter should attach the false muzzle to the coat with a cord sufficiently short that the rifle could not be fired with it on the barrel.
metford rifles were all gaintwist, a feature he felt was an advantage in tearing the patch such that it would fall off the bullet instantly as it left the muzzle.
metford rifling came in more than just the segmental rifling with rounded rather than square grooves.
he had no problem with blowing down the barrel if necessary, suggesting that sometimes dry fouling was an issue, but that the lubricated wad was usually enough when correctly fitting to wipe the bore and soften fouling prior to loading the bullet.
of course they had whale oil in those days as a lubricant in the felt wads.
his bullets were hardened with tin and antimony, the intent being to minimize bumpup only enough to take the rifling, but reduce friction in the bore over softer bullets.
interestingly his breech loaders used only a beeswax wad if we are to believe him, and could shoot 50 or more shots accurately dirty.
not sure if this included blowtubing or not.
walsh, also known as Stonehenge, believed that bottleneck cases retained some fouling that might otherwise go into the barrel.
keep safe,
bruce.

Grisen, 
Yes, the chamber cast shown was made in a Deeley & Edge barrel with Metford rifling.  This is known as segmental rifling.  Think of it as the top segment of a circle used for lands rather than like today's traditional Enfield rifling with square corners.