I'm a handgun guy that merely dabbles in rifles but I do an annual prairie dog hunt and recently came back from that trip, my 5th and absolutely my best yet. So a bit more than five years ago, I had to decide what kind of rig I was going to put together for this and I wanted to do it on a tight budget since I would never be able to hunt these critters any other time EXCEPT on this trip.
I had to opt for .223 Rem, mostly because the the brass supply is 100% both absolutely free and endless, period. Piles of it comes home with me at every trip to the rifle range even when I don't happen to be shooting it that day.
I run the 50 grain Hornady V-Max with a solid dose of H-335 and it gives me a capable 3,200 fps at the muzzle. Prairie dogs are quite small compared to groundhogs and coyotes and none of them at 375 or under survive if I'm doing my part. And a large portion of them are graphically obliterated. There is no suffering.
.22-250 and .220 Swift fans are pulling 300-500 more fps than I am, but I've never felt under gunned with my choice. I actually toyed with the idea of trying .204 Ruger but I've talked myself out of it. Why the .204? Word is that recoil is so slight that you never lose your view through the scope. With my .223 bolt gun and scope at 18x, I lose the view with every shot but if I am set up well, I can regain the image quickly.
I love the idea of the lower recoil .204 but as it truly remains once a year hunting, I'm going to stick with what has brought me so much success.