Assuming that the situation is close to what it's been described as, I think you should:
1. Turn the .380 over to your dad. If they forgot about it and you still have it, you are violating their trust. It sucks but your integrity is more important. If you want to be a man, you have to be honest and tell it like it is. Regardless of whether it's fair or not, if you live in their house you have to respect their decisions and rules.
2. Following number 1, you have to tell it like it is.
Tell your dad that he should have at least been straight with you about why he wanted your access to guns restricted. Tell him that you don't appreciate how he waited until you were away then removed them behind your back. Tell him that he violated your trust and that you were hurt by that and expected better of him and that his actions damaged your relationship.
Don't say it like a little kid.
Don't throw a tantrum like an immature little whiner. Look your dad right in the eye and tell him that you don't appreciate how he betrayed you and that he has some work to do to earn your trust back.
And mean it.
Again, this is assuming that you're not running a con-game for sympathy on the internet and that you actually are sincerely looking for advice.
I assume that you are, because if you weren't you could have easily left out the part about still having the .380, and if you were lying to us, it would have made no sense whatsoever to tell the truth about that.
On the defense thing, it's kind of a moot point.
Everyone on the internet wants to believe they are Rambo, and every 15 year old wants to believe that he's the demi-god offspring of Chuck Norris and Ultraviolet, but that just isn't the case.
Your dad (and mom) should be the ones doing the defending. They are apparently not willing to accept responsibility for that job.
It sucks.
But you're 15. You're probably not qualified for that job either and there just ain't much you can do about it yet.
