Sorry to say, but they likely don't have the mental capacity to process logic behind guns, 2A, cival/god given rights, etc. you won't be able to convince them of anything other than the imotional reasoning that has been ingrained in the mind.
Don't cast your pearls before swine.
Get them the NRA membership though, just to piss them off. Top it off by making a small donation in there name, haha.
“Thoſe who would give up Essential Liberty to purchaſe a little Temporary Safety, deserve neither Liberty nor Safety.” - An Historical Review of the Constitution and Government of Pennsylvania (1759)