What would be really interesting if is some other law abiding citizen with a license to carry pulled his weapon and killed them. Who gets charged with what at that point?
The way the self-defense laws in my state work, the shooter would be charged with murder - assuming these two guys were in fact just walking down the street with shouldered rifles.
We have open carry in my state. Pretty rare you see someone carrying open. Every now and then you hear of someone being arrested for disturbing the peace for carrying open. Our local cops have carry permit data as well. I got stopped recently for having window tint too dark and the office said: "I see you have a permit to carry. Are you armed." I put my hands on the wheel so he could see them and said: "Does a fat baby fart?" He laughed and let me go on my way. I've since wondered where that might have ended up if it was the wrong cop.