Dunno but my guess is the tube is designed to withstand shotgun type pressures.
And in the grenade parts?
Obviously, failure under pressure is the objective but what that pressure is I also dunno.
Thing is, I seem to remember some granades being mostly made of plastic, filled with shrapnel and explosive, so that a hi-pressure body burst is not necessary. Just a speedy drive load.
These things might be very good for printing.
If so, I have a neat design here which will give the fighter the ability to project the thing 100 yards plus, with no actual barrel and material cost of 50 cents or so, fitting in your shirt pocket :).