Oh I've absolutely lost "friends" over the concept of guns and the 2nd amendment, although it's hardly just those two subjects that lead to philosophical rifts. I argued much more when I was younger.
The general ideas of individual liberty and freedom are pretty unassailable in my eyes, so any of the controversial personal freedom issues get me into trouble on occasion. It's why I'm usually more guarded on those subjects. We all know the major topics not to talk about unless you really want to risk getting into it, Guns, Religion, Abortion, Politics, Sexuality, Feminism and that's hardly all.
Even much more minor things, these days, like videogames, D&D, smoking & drinking, or just eating meat can get pretty heated if you encounter one of the increasingly numerous zealots out there... Some are zealots for guns too of course, and I think that's also a problem.
Guns happen to be one of the issues that I personally feel the most strongly about so it comes up the most often for me, and I'll always be quick to put in a good word about the right to carry, right to open carry, that anyone should get a gun, etc... But I've learned to do so carefully and in a respectful way. Going hard never gets the point across and just makes people harden their position.
If you know they're going to specifically have a bias against the NRA, why name drop the NRA? Just hit the high notes and leave the organizational politics off to the wayside. We vilify Moms Demand Action/Bloomberg and IMO rightfully so, but if someone name dropped them I still wouldn't just tear into them and make them dig in their heels. Maybe just say a little bit to open them up to the idea that cool people like target practice, being responsible for their own safety, hunting, or whatever you like doing.
Most people kinda like the idea of gun ownership or are at least willing to consider it when I present it gently, after I've known them for a period of time in which we've been on good terms, and in the light of a fun hobby and pastime rather than going the hardcore political route. I've even taken a few co-workers to the range, one of whom had never fired a gun and wound up liking it.