MTsmith: Out TO 400 yards (and a bit further!) for Prairie Doggin then its rather cut and dried - go with a heavy barreled Varminter in 204 Ruger caliber!
I have been Hunting Prairie Dogs since the 1960's and over that time I have used about every center fire caliber (and most Varmint type factory Rifles!) to shoot them with.
When all things are considered (like accuracy, recoil, barrel heat, barrel wear, reloading costs, flat trajectory, wind resistance etc etc etc!) I would go with the 204 Ruger cartridge - hands down.
In fact I am in the process of purchasing my seventh heavy barrel Varminter in caliber 204 Ruger right now.
That is my recommendation for cartridge - now for a Rifle recommendation.
I am simply enthralled with the fit, performance (accuracy!), barrel length, trigger, thumbhole stock and the solid single shot action of the sadly, now discontinued, Remington XR-100!
I highly recommend this Rifle to you for all manner of Colony Varmint Hunting.
I currently own two of these Remington XR-100's in 204 Ruger caliber (as well as one each in 223 Remington and 22-250 Remington) and that seventh Varminter in 204 Ruger I have on hold right now is also in 204 Ruger caliber.
I have a Ruger #1-V-SS in 204 Ruger with 26" stainless steel barrel, and it is quite accurate and handsome to boot - it does have the laminated gray/black stock. The trigger on this particular Rifle is pretty darn good - not up to the excellence of the XR-100's but pretty darn good none the less.
I have killed many a Prairie Dog and Rock Chuck with this Rifle.
I also have a pair of Ruger 77- V/T's in 204 Ruger caliber and I like the stocks and accuracy of these - triggers are again pretty good.
I also have a Remington 700 VLS in 204 Ruger and it was one of my first 204's and one that shoots VERY well indeed - right from the get go that - and it continues to do so to this day.
I don't think you could go wrong with any of the above listed Rifles for Prairie Doggin.
All you will need to gear up for the 204 cartridge/Rifle is a new cleaning rod, a set of dies and some Berger 35 grain bullets or some Sierra 32 grain BlitzKings - then go "to town"!
Best of luck to you with whichever cartridge/Rifle you choose.
Hold into the wind
VarmintGuy