They were generally lifting, but one did shoot off and hit my mate on top of his napper and then caught in his hand

They seem OK ATM. I think there were three factors which I think you have highlighted all of them
1. Change in room temp. It's in mid 20'sC of an evening currently.
2. Maybe being a bit too generous when filling and not allowing room for expansion
and
3. The one you just mentioned, stoppers not being the best fit, though I don't think it's the stoppers more like the cheap chinky bottles maybe not offering the best of fits. Probably why I got them so cheap.
Not a lot I can do about 1 & 3 ATM but I reduced the amount of spirit down to the absolute base of the neck and they seem OK for now
