I used to have a 9x18 Makarov. Those could be annoying mixed with 9x19, because they didn’t really look any different. Case heads are the same size, length is only 1mm off.
A 9x18 case loaded through 9x19 dies would act just like a 9x19 right up until the firing pin hit the primer. The firing pin would just push the cartridge forward in the chamber, since the case mouth was just floating there, and not fire.
I think .380 is better than 9x18; I can see the difference and sort them easier.