Why does Reid carry a revolver?

There doesn't seem to be any official answer online but there has been lot of speculation and theory. I was in the process of adding a comment of my own opinion when I found the following from IMFDb.org which seems to be a copy and paste from a message board but brings up some possible answers.

I won't paste the text here but in summary it mentions two possible reasons for the switch. Namely that it may be a nod to Silence of the Lambs in which Clarice Starling has a similar weapon, and it also may have been a decision by Mathew Gray Gubler to choose a weapon that he felt better suited his character's tastes, which he also uses on his personal life.

My personal thoughts were along the same lines. The best I can do is speculate but based on what I know about the character and his history is that he was at first uncomfortable carrying a service weapon and there was a story arc dealing with him becoming comfortable with his weapon and being confident in using it when needed. Based on this I would say that the revolver was likely a weapon that he ultimately became most comfortable with. They are more reliable and require better precision due to the limited amount of ammo they can hold.

When Reid carried the semi-automatic in its ridiculous position, an unsub told him someone would take it away from him. Maybe that little gem stayed in the character's mind, and he made a wise switch. He does look a little like Wyatt Earp now with the revolver.

It could be a number of things. I am a 5'2 stout female with small but square hands. I don't have willowy fingers and narrow hands as with most women. Though my weight is adequate to hand a .45 semi auto, the two times I test fired one it a) few out of my hands and then b) the recoil cause me to punch myself in the forehead. Reid has long hands and long fingers. Maybe he needed a gun with grip that he could hold onto but was still powerful. As for myself, I was great at archery as a kid so I will be sticking to a Mongolian Horse Bow and my trusty fireplace poker.

I'm a firearms instructor with some law enforcement experience and keep track of what the typical duty weapons are for major LEAs (law enforcement agencies).

I don't believe the FBI has a grandfather clause for approved firearms. Once the FBI changes approved firearms, agents are required to turn in their service sidearm for the new approved service sidearm. The fact that Gideon, Reid and Rossi are allowed to carry something other than a Glock in .40 S&W is a technical error; a major one to a firearm savvy person such as myself.

Revolvers have not been approved for use by FBI agents since the Miami FBI Shootout of 1986.

On the alleged competition shooter who stated revolvers are reliable. Wrong. All you have to do is to bend the crane or extractor rod and the revolver will not function and will require a gunsmith to repair. If the cylinder ceases to rotate on a revolver for any reason, it will no longer function. A tactic to disarm someone with a revolver before the hammer is cocked and the cylinder has rotated is to grab the cylinder. It does not take much grip strength to disable someone with a revolver by grabbing the cylinder before the cylinder has rotated to fire the next chambered round in the cylinder.

The advantage the revolver has over semi-auto pistol is that an experienced shooter such as Jerry Miculek can empty a revolver cylinder faster than someone can empty the magazine of a semi-auto pistol.