This goes back to the beginning of the auto 5 production in 1903. John Cockerill was a British Industrialist whose company supplied high quality steel to Fabrique Nationale (FN) which was the maker of the A-5. The Cockerill name was first used on Browning barrels stamped "cockerill steel". The steel was a very strong quality that met the proofing requirements of guns that were shooting smokeless powder. Eventually the Cockerill name was dropped from the barrels and "special steel" was used instead. The FN guns that were not sold to Browning in the US, uses the barrel stamp of "acier special" which means special steel in the French language.
You will have to ask Browning.
Haven't seen that marking. Choke markings on Browning shotguns are coded by a series of asterisks and dashes. They also had a marking called 'ACIER SPECIAL' which simply means special steel, indicating the gun was suitable for smokeless powder.
Assuming you mean a barrel that is for lead pellets, if the barrel is not rifled, steel shot will not damage the smooth barrel. If it is rifled however, steel shot will in fact damage the rifling.
The serial number of the weapon.
Browning Choke Markings "* " = full "*- " = improved modified "** " = modified "**-" = improved cylinder "**$" = skeet "***" = cylinder
This is the weight in Kilograms of the barrel by itself.
Steel treated to have blue color
It stands for 'Nickel Steel', the material the metal is made from.
They are a code used to denote choke size.