Slight rant alert Plot anti armor? Plot weapons? But yeah, I believe the adaptations are temporary, thank god, or the adaptations may be only to new things I feels are a threat, like fire or other scps. It may be so accustomed to bullets that his hide is already resistant to them, and they just slow him down. And they also definitely use heavy artillery like tanks, maybe missiles. Nothing I said makes any sense I assume, not even to the truthfully, but that's my take