been looking around and i think i found my answer that the not for pressure PVC is not good for spud guns. Still does my "ignitor" look safe?

i went to my local home depot today to make my first spud cannon... and i was planning on a 4" expansion chamber with a 2 inch barrel. The problem that i found was that all of the PVC pipe that was 3" or bigger had "not for high pressure" or someting like that. It was Schedule 40 but i was too scare...