Two questions / observations
#1. Instead of approaching the fellow who called the RCMP with a lynching rope, why not approach with an olive branch and calmly find out why he called the police. Was it due to ignorance and not knowing the status of AR15's, possibly believing that they are machine guns and illegal or was it in spite. If it was due to ill intention, find out why and determine if something can be done to overcome this.
Education, cooperations and calm approach would most likely result in a win/win situation as compared to creating a divide among gun owners. Do you want to create another anti-semiautomatic gun owner.
Remember that he/she as well has friends and will be teling them thier version of events.
#2. If you arrange a "blackgun" event, would it be a good idea to invite the local cops. There are those who are into firearms but may have not shot a blackgun. There are those who may have only handled their issue sidearm. Invited them (no cost to come), befriend them (let them shoot any and every style, make, model you have), educate them (laws regarding the classes of firearms) and show them a good time.
I would suggest that you have an "adopt a cop" program in which a knowledgable person be with every group to ensure the proper idea, information, firearms handling and safety is being diseminated. You want them to leave with a smile on their face and assured that the firearms community is knowledgable, supportive and practices safety first.