Please be aware that you shouldn't use .380 +P ammo in a Glock 42. Why?
- Unlike many other rounds, there is no standards around .380 +p pressures and I'm not aware of any manufacturers that endorse the use of .380 +p.
- Glock does not endorse the use of .380 +p rounds. It may not cause any damage to your firearm, but it also may not work properly.
Since the .380 is considered a marginal self-defense round, there has been a long-standing debate about using FMJ (solid) vs. using HP (hollow point) bullets. Unfortunately, .380 FMJs tend to over penetrate, while most .380 HPs tend to under-penetrate. ShootingTheBull410 has done an excellent series of YouTube video's providing detailed analysis of .380 HP rounds. I understand if you aren't enough of an ammo geek to want to view all of the details, but the OP should at least view his "best of" selections.
[video=youtube_share;GNtPHYwcDts]http://youtu.be/GNtPHYwcDts[/video]
The original .380 tests were done in 2013 with a micro pistol, but ShootingTheBull410 did an update for the G42 in 2014 that didn't change the results significantly.