we stopped selling these fun things because of the 20mm rule
we used to do tennis balls for the dogs and golf balls wil 308 blanks
sigh, find a readily available ball that is 19mm and we'll sell 19mm launchers
Maybe market them as being just stupidly heavy muzzle devices whose benefit is bringing a rifle's centre of gravity forward for PRS balance. There are days when a pound or so of iron or lead with a threaded hole in the middle could be ideal to get the rig to balance on a barricade.