Warning: We're not experts on safety, tools, or construction. We hope that what we write here will encourage you to look into safety issues and make your own good decisions.
Even when loaded with "blanks", firearms can wound or kill. Don't risk it!
PVC pipe is inexpensive and easy to get, so it is tempting to use it for compressed air. This is a dangerous practice.
As in any field of human endeavor, you will be faced with numerous choices. Should I do it this way, or that way? If one way is safer than another - choose that way. If the "safer" way isn't completely safe - don't do it at all.