This 'cannon' was evidently well engineered and used a Swedish Bofors barrel to fire the baited line out to sea.
40MM Bofors Anti-Aircraft Gun.
I am very saddened that such an "accident" has claimed a life - strict adherence to the basic firearms safety rules may well have prevented this death.
TREAT ALL GUNS AS LOADED AT ALL TIMES.
NEVER POINT A GUN AT ANYTHING YOU DON'T WANT TO DESTROY.
HANDS OFF THE TRIGGER UNTIL READY TO SHOOT.
Down here I've heard of folk Surf-Casting using 'kontiki' Rafts to carry-out their line - story goes that you use a boiled sweet to secure the baited line until the wave action dissolves the sugar and away you go fishing.
- A decent off-shore wind and plenty of baited hooks should produce a feed.
I've also seen a home-made "cannon" built from heavy steam pipe that was an attempt to launch a steel spear or harpoon to propel a baited line out to sea beyond the surf line. These guys were using 'Blasting powder' (coarse black powder) as a propellant and seem to have survived long enough to re-think and abandon the enterprise while they were still intact.
There are commercial line casting 'cannon' built that use compressed gas to fire a slug of frozen bait way out to sea - such as the SandBlaster BaitCaster - a kind of potato gun.
While no doubt costing plenty to set-up - I'd say its size and launch system are considerably safer than trying to build a firearm type cannon to do the job.