Several years ago before he went to work for NATO, my grandson worked for a private arms development firm. He was tasked with developing a new 40mm grenade, for use in a launcher.
First off, he had to build his own launcher. Then after tests confirmed the efficacy of the round, he used an M-19 launcher (as he had used in Iraq) to demonstrate it for use in auto fire.
Shown here, assembling "one off" hand built launcher, with chrony. Also shown, shoulder fired 40mm launcher, with new rounds.