As with Damascus patterns, I think folks called barrels whatever they wanted
Hunter Arms introduced "Nitro" Steel in 1898.
In 1913 Lefever had "Royal Nitro" on G and "Premier Nitro" on F.
The J. Stevens Arms & Tool Co. Model 270 was listed with "Nitro Steel".
After 1904 the lower grade Tobin doubles were fitted with DeMoya Fluid Steel and "Trojan Nitro" Steel.
The 1920s Folsom/Crescent American Gun Co. "Midget Field Model" was listed with "Nitro Steel" barrels.
The 1907 Union Fire Arms catalog listed the Model 22 double with "Imported Nitro-steel Barrels".
And this Hunter Arms Co. Fulton tradename New Haven Fire Arms Co. for E.K. Tryon and Great Western Gun Works has "London Fluid Steel"
Other Fulton tradename guns had "Superior Quality", "Royal Steel", "Peerless Steel", "Fluid Blued Steel", "Projectile Steel", "Silver Steel", and "Missabe Fluid Steel" on "Comstock Arms Co. Duluth" guns. The Mesabi Iron Ore Range is the largest iron deposit in NE Minn. Lake Superior Iron Mines owned the Duluth, Missabe & Northern RR. The Marketing Dept. in Fulton must have been proud of that one!