Once a system had been devised for making malleable iron rails, around 1819, the rack and pinion motion became unnecessary, apart from later use on mountain railways. However, until that time it enabled a small and lightweight locomotive to haul loads totalling at least 20 times its own weight. "Salamanca" was so successful that Murray made three more models. One of these was known as "Lord Wellington", and the others are said to have been named "Prince Regent" and "Marquis Wellington", though there is no known contemporary mention of those two names. The third locomotive intended for Middleton was sent, at Blenkinsop's request, to the Kenton and Coxlodge Colliery waggonway near Newcastle upon Tyne, where it appears to have been known as "Willington". There it was seen by George Stephenson, who modelled his own locomotive "Blücher" on it, minus the rack drive, and therefore much less effective.