The trio, all serving soldiers, raised the money through sales of their debut release and a sell-out UK tour.
Now they are inviting servicemen and women based in Helmand province to add their voices to two tracks for their next album, due in October.
BFBS (British Forces Broadcasting Service) Radio has already put the word out to soldiers stationed at Camp Bastion inviting them to sing on new track I Will Carry You, a song dedicated to soldiers who risk their lives each day.
They will also feature on a cover of the Rod Stewart hit You're In My Heart.
The group – Lance Corporal Ryan Idzi, Staff Sergeant Richie Maddocks and Sergeant Major Gary Chilton – handed over 271,000 to the Army Benevolent Fund, the Royal British Legion and Help For Heroes charities at Kneller Hall in Twickenham, south west London.