POLAND_SPUD wrote:well yea but that's doesn't sound very practical, right ?
this thing is going to be expensive, loud and powerful so it's best to make him aware of all this... also this thing is going to attract a lot of attention if fired close to habituated areas
Once again, practical?
Practical is a relative quantity, and it scales as the inverse square of affordable and feasible to build.
Turning a few thousandths off a 2" aluminum or steel bar and drilling a hole in the back to stabilize it doesn't take very long. Aerodynamic darts are obviously another matter, but they're not a 5 minute job for any bore.
Driving a bulldozer into someone's house will attract a lot of attention too, and ranks very close on the crazy scale to firing a 150kJ gun in a populated area.
One thing to look out for is that the internal diameter of most tube is not a guaranteed quantity, and can be off by as much as a millimetre for the larger tubes. If he gets lucky on the internal diameter of the barrel, it'll be perfect for firing 2" ball bearings and 2" rods. If not, then any projectiles will need to be turned (or perhaps cast).
POLAND_SPUD wrote:or a small shed, right ?
From experience with my 100kJ gun, I assure you that unless the small shed was well stocked with sandbags and concrete blocks, it wouldn't be much of a contest.