Bear spray expiry dates: good news, and comical peer-reviewed pseudoscience

Last year my 4-year-old can of bear spray reached its expiry date, completely unused, and I wondered how sound the basis of that date was. Reddit showed plenty of others wondering or asserting on the matter, several outdoorsy sources reported on testing, and there was a journal article from researchers at Brigham Young University.The good news starts with: the active ingredient, capsaicin, does not degrade.It continues with: the other big concern is propellant leakage - and you can check that by weighing the can. Mine weighed 300g new (contents 225g), and still weighed 300g four years later. Bear Beware Solutions, based in Alberta, suggests discarding the can if the weight drops below 75% of original.Unfortunately, none of the sites that tested old cans bothered to weigh them - so when there was sub-par function, we don't know for sure that they had leaked, and were underweight. (CBC news reported that two of four old cans produced thick, comparatively feeble streams, and mentioned that the nozzle fell off one of them, but they pushed it back on and tested anyway.)Some sites did suggest a brief annual test fire to verify that the stream was up to par; I went with that. I sprayed a decent blast - about half a second, I reckon - and it was impressive: a vigorous yellow cloud, blasting out perhaps 6 metres. The cans hold about 7 seconds' worth of spray, and when I weighed mine it was down by 16g - 7% of the net weight, consistent with 1/2 second. So I'll be able to test 5 times before hitting Bear Beware's suggested limit - which will double the lifespan of the can.The journal article: babes in blunderlandAn Investigation of Factors Influencing Bear Spray Performance | BearWise (Journal of Wildlife Management, 2020)This article had me scratching my head right away: the abstract said things that just didn't make sense - notablyWe… documented that bear spray head pressure declines in a logarithmic, not linear, fashion; over half of a new (7‐sec spray time) canister's pre