You guys are thinking like what you are Cannoneers , the Brandt/Stokes design is Not a Cannon it is a Launcher !
While the energetic is the same the mode of operation is different , a Cannon/Cohorn /BP Rifle/shotgun are direct contact energetic propelled while a Launcher deals with the impingement force of the energetic in a different way, it is a Low pressure /Hi capacity gas expansion chamber design ,that is why they are far more lightly built .
Launchers use less energetic with a lower mass projectile and Lower recoil by design ,Launchers operate very differently than Cannons !
Air gap in a Cannon is a dangerous thing they are designed to be in contact with the projectile ,a Launcher on the other hand is more like a Blow gun and driven not by the contact explosion but instead by the expansion of gas produced by the energetic into a volume at a much lower pressure and velocity .
Example the M-203 modern Launcher the case is a Hi /Low design ,a Hi pressure cartridge with a burst disc to get complete burn of the powder ,the disc bursts expelling the gases into a chamber under the projectile at a Low pressure but continued expansion propelling the projectile down the barrel resulting in Low recoil forces and low velocities .
It is based on the Brandt/Stokes design principals for a Launcher , Very different from how a cannon /cohorn /rifle/shotgun is designed to function . Yes they use the same energetic but in a different way of force application .
My shear link tube is designed with a predictable fail safe should anything go wrong instead of a catastrophic shrapnel filled danger zone ,if you are standing 5' away from it it might singe your pants cuffs and you might catch a few hot embers but you will not get Any metal shrapnel !
Two totally different principals of operation using the same energetic .
I am Far form
Crazy !