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Found 25 of these at the beach I work at this morning.(r/whatisthisthing)
Just to add – if they’re nitrous they’re meant for a whipped-cream charger, like these.
If they’re CO2 they can be used for air pistols, fast bike-tire pumps, and various other uses. In a high school “tech ed” class we used them to propel wooden race cars.
I agree with /u/calum_morton that these are likely (edit) NO used for whippets, though I guess someone could have been having a seaside airsoft battle last night. There might be markings indicating which they are.