I thought it was either an healing or an instant death bullet, that doesn't leave traces, when he shoot it on dead objects. Imagine it would have been the second one. "I have enough Hp. I test it on my arm."
And this chapter tells us something we already knew multiple times EMILY IS HANDS DOWN THE BEST GIRL.
Ryouta, seriously, stop being such a manlet and kiss her, because she freaking deserves it, she's the best girl in this world and no one can come close to her.