I personally wouldn't let that effect a friendship. People are multi faceted and it definitely doesn't mean he is a bad one. I just feel people are so misguided and don't realise that winning the debate is meaningless.
I always think the easiest tactic is to ask whether they think gun restrictions would save even one child's life, if they say no then direct them to statistics from Australia and the UK and if they say yes then it is the end of the conversation.
They just say smaller populations and the fact the UK and Oz are islands so it wouldn't work because blah blah blah....