This is a 40mm mortar made for a potato cannon with a barrel made of 1.5in 40sch PVC pipe. This uses a #209 shotshell primer. Use a 1/2in flathead common nail. Set the primer and glue in the stopper, then fill the inside with the explosive of your choice, glue it up, stick a nail in it and fire!
Disclaimer: This is for prop use only! I am not responsible for any actions and consequences you take from this 3D model, including what it is intended for (prop use).
Note: This was inspired by a TKOR video, RIP Grant Thompson.
Note: I have printed this and the pieces do not not fit together due to high tolerances, I will put the link to the tinkercad if you need to modify the dimensions: https://www.tinkercad.com/things/6P2xIpWIuqS-15in-mortar-shell-40sch-pvc