Twice now they've had to re-roof this building --hail damage.
The roofers would push their nail guns against the shingle, it would go off on contact, the recoil would lift the gun off the roof, the roofer would have applied force on the nail gun to slip it sideways to the next stapling spot, the nail gun would make contact and fire again.
Four of these operations would occur in rapid succession and it would sound bam-bam-bam-bam in about a second, like a machine gun.
A couple of guys working on a section of roof and it would sound like a mid-1920's gun battle.
Terry, 230RN
September 2017, pic taken from my balcony: