It was clearly unhealthy at first how Bruce kept thinking about the weapon that Matches Malone  used on his parents, the weapon he used on the man when Selina made the noise to make him drop his gun.. 

This gun was never fired at me, but it still scarred me for my life. I grew up broken and sad after this hunk of metal took everything from me. And who knows how many other lives it's ruined? Or ended.

The one he picked up, and kept in his hand until Jim pried it gently out of his grip.. He tried on his own to take it from the GCPD evidence room, and failed. So he called in a favor from a friend to get his hands on it. 

It could have ended up as a twisted thing, a reminder, a trophy or something to use himself. On Countless others in the exact same way.. Instead Bruce forged it into something else.

I'm going to make that metal pay for its sins. I'm going to burn the metal that killed my parents. And forge it into something useful. So the metal that broke my heart as a child? That same metal will protect my heart as a man. And That is justice

Buce couldn't promise that he wouldn't never use it to hurt someone. The metal protected his chest from gunfire but the symbol could come off his own personal use.. As a last resort personal weapon..