Instead of quoting ACPs whole post I will just post below it. Special Agent Edmundo Mireles, Jr. was seriously injured and walked up to perps the car in an act of pure bravery and ended it with 5 hits from his S&W 686.
It was such a public stain on the FBI that it led to a whole bunch of changes, most notably all auto pistols in 10mm and an advanced ballistics program. That is "Why is the FBI's choice of gun given so much attention". In reality it should be "Why is the FBI's choice of AMMO given so much attention?"
Because they spend a lot of time and money testing guns but mostly ammo loads. They have a budget for this that is unmatched by any other entity.
Long story short I was in a 24 hour CVS at about 4AM a couple of years ago. There was an older man who was well dressed and his jacket was open. I could see he was carrying in a shoulder holster. I asked him if he was a local PD detective and he said no, I'm FBI. Like a fool I responded "Yeah right". He showed me his honest to goodness FBI badge and I said I'm really sorry. "Have you robbed a bank lately"? Umm No. Then don't sweat it. Condensed version there was a Dunkin Donuts in the same mini mall and I asked him if wanted to sit down and have some coffee and donuts, my treat for insulting him. He said sure and thus began my schooling into FBI protocol.
Long story short, he was carrying a wheel gun, the old timers before a certain date are allowed to carry what they seem fit. They are grandfathered in. He said if his machine gun of choice was a Thompson sub gun when they made the rule, he could have that in his trunk. He had a 686 snubbie and that was his primary sidearm. We talked about the Miami shootout and I cannot repeat his exact words because of this forums decorum. He recommended some books to read and said that actually nobody REALLY knows what went down that day, it was complete chaos and a tactical blunder on the FBIs part. The other 6 agents should have never been separated and cut off. They had the heavy firepower that would have ending it quickly.
Anyway every now and then I run into him. He will be retiring later this year. He trusts his .357 magnum and has never had to shoot it at anyone. It has really been a very cool learning experience and led to many insights on the FBI. They are definitely not "armed accountants". They have a budget just like anybody else. For the newer members of the FBI, yes they are given guns. That is bid out just like everything else. They don't have a blank check. When the FBI purchases weapons they buy 15,000. Everybody wants that contract.
The things you learn when you are buying a bottle of aspirin at 4AM.