21 Guns by Green Day is in Bb at 84 beats per minute and runs 5:00 across 59 bars. It uses 6 chords — Dm, Bb, F, C, A, Csus. The chord diagram changes as the song plays and the words light up as they are sung, so you can strum and sing along without reading ahead.
Want the melody line note by note? 21 Guns guitar melody tab.