Total solar eclipse over Wyoming. Wyoming will be a popular choice for eclipse chasers because of the good weather prospects, Uncrowded highways (outside the Jackson Hole area), and good duration of totality.
The 9x18 bullet is .008 larger than the 9x19. The 9x17 (.380 ACP) is a straight case that may insert part of the way into the chamber. If you misloaded the case would be jammed in and not fully chamber, so it would not fire. The 9x18 is enough larger it probably would not enter the chamber. know a 9x19 will not fit in a 9x17 mag, what would happen if a 9x17 was chambered and fired in a 9x19. My whole family has 9x19's in various frames, except my girl friend did not like it and went with a 9x17 and I am concerned with cross loading and having a 9x17 chambered into a 9x19.
Most people who casually reference 9mm probably mean 9x19mm. However there are a number of kinds of 9mm ammo to include: 9x23mm, 9x25mm (actually a necked down 10mm), 9x18mm Makarov, 9mm Browning Long, 9mm Largo, 9x18mm Ultra/Police (not the same as Makarov) and in some places 9x17mm is the name for .380 ACP.