yeah i spent 7 years in the army and 15 years in federal law enforcment before moving to Canada.
All i can say is the pup is lucky it was buck shot, otherwise he wouldnt be alive.
Buck shot doesnt spread until it leaves the approximately 20-30 feet or the barrel .
Close range 5-15 feet you would have something that looks more like a hole as the velocity v's range hasnt allowed spreading.
In my experiences the shooting of someones dog or pet is associated with a random moronic act with no reason (peer pressure from kids being tough with there mates) or someone trying to upset you personally, like an ex girlfriends new boyfriend or someone you delivered a bad beat too (revenge).
Either way it really is a weak ass act. I have often said laws are just not strong enough against these type of offenders. I always prefered to annoy them a little more.
Hope he gets better quickly.
Steve
P.s one thing an offender doesnt want is detection. for 100.00 you could place a very obvious CCTV camera near your dog and hook it to your PC. I have a couple around my house so I only have to answer my door for friends.