Wow. First off, you did fine. I disagree with Creature's approach, although if it works for him, that's super. I was the mother of four children ALL of whom were tantrum-ites, and DURING the tantrum, the communication is all one-way...going from the tantrum TO everyone else. It's not until he calmed down that you could talk to him at all. Creature thinks the conversation should have happened at the side of the road. I'm with those who think that letting him out and letting him walk a couple of miles to cool off was a very good idea, particularly as it was his choice.
I have no brothers and sisters, but my husband has four. One brother is a shooter. The other three are various states of hysterical antis. Thing is, we all get along just fine, because nobody is committed to changing anybody else's opinion on this. We who are gunnies don't talk about it around the hysterically anti sister in law. This means that all of us, on both sides of the fence, have long ago realized that there are some issues to just shut up about around some people. We don't talk religion either. And we all get along.
Your brother needs to grow up and take responsibility for his behavior. He can have his feelings, but unlike what we were all taught in the last 30 years, HAVING a feeling and EXPRESSING the feeling are two different things; and frequently the second is a mistake.
For your part, don't stir the ant pile, don't take him by the gun store again, don't bring it up, and if he brings it up, respond with something like "So! How about those Dodgers!" Make it clear you're not interested in playing when he wants to engage on this. Be friendly, don't try to enlist other family members on your side. And don't budge one single solitary inch on your gun ownership either.
Good luck. This is a tough row to hoe.
Springmom