I have a Weatherby Vanguard Varmint Special (Howa action) in .223 Remington with the 1 in 12" twist. It shoots 55 gr bullets very well as well as anything lighter. I prefer the 1 in 12" twist rate, because I prefer to shoot the lighter bullets as fast as possible at safe pressure levels. My standard load in the .223 is either a 50gr bullet at 3300 to 3400 fps or a 40 gr bullet at 3600 to 3700 fps. I don't think the faster twist barrels can achieve these velocities without pushing the pressure. I haven't tried any heavier bullets, but I believe it would shoot the 60 gr Nosler partition okay since it is a rather short bullet. If I want a bullet heavier than 55 gr, I will use my .243 Win. If you shoot nothing smaller than groundhogs, maybe you should consider stepping up to the .243. I use my .223's on ground squirrels, prairie dogs, rock chucks, and up to coyotes. Anything bigger gets at least a .24 caliber bullet. At least so far.