Here is the full list of all 12 Rock Band Metal Track Pack achievements worth 250 gamerscore.
Play "D.O.A.", "Laid to Rest," and "Hair of the Dog" in Solo Tour
Hit 100% as a Bassist on "Closer," up-strums only
5 star "Master of the Universe" with any instrument on Expert
Finish "Thrasher" as an Expert Drummer
5-Star "Blinded by Fear" on any instrument... with your eyes closed
5-star "Red Devil" as a Vocalist in Solo Tour
Score 100% as a Vocalist playing "Forever"
Complete "Transmaniacon MC" as a full band, with all band members on Hard or Expert
Play "Screaming for Vengeance" in a Score Duel
Get 4 stars or better playing "3s and 7s" with a full band
Complete "Killed by Death" on Expert without a band member failing
Complete Band Tour on Medium difficulty or greater