I am assuming that since the diameters btwn .380 and 9mm are the same, that one would use a 9mm .355 bullet seated in a .380 case with the appropriate powder charge.

Yes but I would stay to the lighter end of the bullet weight.

No trouble at all just make sure you use the proper power weight for the weight of the bullet.

I reload .356 lead TC 122 grain bullets in my 380 ruger LCP

My load is

Win brass
Win sp primers
Win 231 = 2 grains
C.o.l. .960

Chrono'ed a fast 562 fps lol

Shot 250 out of my ruger so far. Zero problems

Jason

not problem, i use bullet Pb TC 122gr with 3.7gr Accu. No.5. OAl is 25mm and energy 240J. Function in my Beretta 84 perfectly.