Barm: I have only shot a few Rock Chucks with my two Varmint Rifles in caliber 221 Remington Fireball and as I recall they were DRT.
I use the Berger 40 grain hollow-point in my heavy barrel Kimber of Oregon Ultra-Varmint - and then I use the 40 grain Nosler Ballistic Tips in my Remington 700 Classic.
I mostly use these Rifles on Prairie Dogs and Ground Squirrels and these bullets sure shine there!
Best of luck in finding a more reliable "pill" for Ground Hogs.
Hold into the wind
VarmintGuy