Can someone saying that a shotgun is insufficient please explain why a semi-auto rifle is better.
Limited to 40 yards? Only 40 yards? Most HD/SD scenario even in a rural area is gonna be like 5-15 yards tops. If he does get to the exterior of his house while he sees them on his property, that distance is just that, maybe 30-40 yards. Also, slugs are effective to about 100 for anyone who's a decent shot. But how many SD scenarios take place at 100 yards???
Think about that for a second. Say a burglar IS coming to his house. They drive a truck down the road, park near his house, and sneak inside. Now the incident occurs at room's distance. What are you going to do, shoot any unidentified car coming down the road from 150 yards away? Have fun explaining that one to the jury.
As far as the criminal being armed, they're after your stuff, not bent on murdering you. Yeah sure, every couple decades you run into some In Cold Blood types like the guys in Kansas. But the significant portion of the insignificant odds of being robbed will be a person after your stuff. Killing or harming you would be something that occurs if they perceive you to be interfering with that.
A shotgun is just fine for HD. More important for his home security would be a good alarm system, a dog, a gun safe, a safe for valuables, good lighting outside, etc.
Not that I'm trying to compare, or brag, or that me living in peril, makes this somehow better. But do consider this. I live about 3 miles from high rise housing projects. 14 stories of scum, drug addicts, weirdos, vagrants, losers. My town has not had a violent burglary in 18 years, and before that, who knows.
I'll leave it with a question:
How many burglars mount an attack from 150 yards away with a rifle?