Something else that crossed my mind when writing this was a way...

Something else that crossed my mind when writing this was a way perhaps to be able to have more than 3 x 40mm rounds in the barrel, what if you had say six or even more rounds in a longer barrel and using the recoil have a ratchet mechanism where the breech block at the rear ratcheted forward one round space every time a round was fired, this would also allow the same barrel length for each firing, which may help with accuracy? just a thought!