His choice of weapon, a FN 5.7 pistol says a lot about his intent and state of mind. Not the first choice for plinking, competition or home defense for that matter.
The amazing thing to me is that..
A. He found so much ammo for it.
B. He was able to afford it.
A single Major living in a dumpy apartment has a LOT of discretionary income. When I was a married Captain, my ex wife and I deliberately looked for a place that was well below my basic allowance for quarters, and I had no problem plunking down cash for a lot of little luxuries including a .50AE Desert Eagle which listed at right around $1K at the time + plenty of ammo, which even back then was about $1.05 x round.
I know the 5.7 is still a bit more obscure, but a single O-4 that finds a cheap apartment off post has some $$ to do with as he pleases.
It's on sale at Cabela's, item # 9IS-216819, $100 for 250 rounds, cheaper if you order more. I'm sure an MD with salary of $100K/yr, living in a doghouse, having no family and no hobby, could afford the gun ($1000) and as much ammo as he needed.