No. I’m asking for citations when your assertion is that flammable hydrocarbons mixed with oxygen in an enclosed container and ignited can not exceed 30-40 psi, or the bursting force of said (often brittle) plastic enclosed container. Especially since garden variety Schedule 40 PVC in the sizes we’re talking about are rated (non-shock) for over 180 PSI and many into the 200+ PSI range but there are easy to find videos of them bursting in spud guns.
[https://parts.spearsmfg.com/sourcebook/SCH40TECH_40WHTPIPE-1...]
And as noted in the prior declassified paper, shock fronts from these mixtures can easily move in excess of 280 meters/second even unconfined in air, with the right mixes.
Goofy? Perhaps.
Life altering? Perhaps [https://youtu.be/KqstP9ics2A?si=Omtp8N7xPW91A5TU] - and yes, while many of those failures in the video are clearly due to improper glued joints (which is a big hint at the pressures involved, and way better than other kinds of failures!), many also involve the PVC shattering. Several in the first few minutes, actually.
I made a ton of potato guns as a kid, btw. Typically using propane. But I always respected the forces involved, because I wanted to not lose an eye, kill anyone, etc.
Looks like some enterprising MIT alumni + the air force academy did some internal ballistics reseaerch [https://arxiv.org/pdf/1305.0966].
Note - I highly recommend against using acetylene, which they did for some of the tests, as it will perform a proper super-sonic detonation [https://www.icheme.org/media/10611/iv-paper-08.pdf] under the right conditions and turn your potato cannon into an IED even if the projectile moves, or potentially even with no projectile at all. Per that paper - “It appears that Acetylene is unique in that it will propagate a detonation at initial pressures below those of which it is capable of sustaining deflagration”. I would have checked this paper which even more directly addresses the topic [https://link.springer.com/article/10.1007/BF02671917] (because I love this kind of thing, obviously), but $40. :(
So looks like as long as everything goes well, they are in the approximate range of 20 psi while driving the projectile, except for acetylene which hit a hair under 90 psi. They used stoichiometrically ‘perfect’ mixes.
My guess is the failures in the videos (and anecdotally) were driven by too lean fuel mixtures, easy to do in some conditions. But this paper [https://www.scientificbulletin.upb.ro/rev_docs_arhiva/full14...] seems to indicate the opposite, and also pressures >= 120 PSI. So I don’t know.
I also saw MAPP gas apparently being used in one of them too (the yellow cylinder attached to a plumbing torch), which would also be unwise.