Attachment 128611
.380 (red spring on the right) fits the 9mm slide and the action can be hand cycled. It is considerably lighter, though. Hard to say how much without a spring tester.
I'm not sure I would use this for anything other than very sub-minor loads, if at all. It might be interesting to try with that reduced Hornady 100gr critical defense load. Factory says 100gr / 1125fps, and I think .380 averages something like 95gr / 955fps. So similar weight and 175fps difference in velocity. Of course I have no idea how it performs in gel. Even if it cycles the action without damaging the gun it might be pointless.
I still think we'd be better off with an official .380 +P designation and the big 3 loading up to that rather than trying to load the 9mm down.