The difference is?

Chrome moly is the steel recipe chrome lined is the harder than steel surface inside the bore and chamber.Bushmaster uses 4150 chrome moly vanadium steel that is chrome lined and the steel is also a hard excellent quality grade.Some manufacturers us chrome moly steel like wilson combat but its softer 4140,RRA uses the same but chrome lines some of their barrels.The harder steel takes heat a bit better but I dont think it matters as long as they are chrome lined,chrome is 2x as hard as steel so as Troy syas"Go chrome or go home"