If you consider yourself a Christian and act in self-defence, you don’t truly believe
Actually, instead of owning a gun to “defend against a baddie”, you should welcome anyone who holds a gun to your head, because they’re about to bring you to God.
Ecclesiastes 3:4 - "there is a time to kill and a time to heal"
Don't only look at one part of the Bible. As important as the gospels are, you need to look at all of scripture to get the full picture. Yes, "turn the other cheek" and "give them your shirt as well", but do those as part of loving your neighbor as you love yourself.