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A chat on subreddit /r/wallstreetbets
human
Isn't full metal jacket the most likely to penetrate armor?

gpt
Disclaimer: I'm not much of a gun expert. 
  
 It's not bad, but it's not armor piercing either. Heavier rounds than 115 grain would also be somewhat more likely to penetrate. 
  
 I don't think they intentionally made the test easy (past using a 9mm pistol instead of a rifle...), just that they weren't trying to claim 'it's bullet proof' so much as 'we shot it with this, and it didn't penetrate'