Far and away the best bullet I've used for prairie dogs in my 22-250 is the Speer TNT 50 grain. Not that it was the most accurate but that it was accurate enough, had the "red mist" effect I like, and was a budget type bullet purchased in the 1,000 piece carton.

The most accurate was a 50 grain Berger and then the Nosler 50 and 55 grain B-Tips and then the Hornady 50 grain V-max

Be very careful to blame the shooting on the bullets.....it just might be in the gun's bedding.