The factory rate is 1-12", but that's "nominal" as a lot of button rifled barrels vary a bit to the slow side. Over on .204ruger.com, several of the guys measured their twist rates, and some of them only made it to 1-12.5", and guess what? Those rifles didn't like the 40gr. Hornady bullet at all. It's a bit too long for those rifles. Some would shoot the 40 Nosler "okay", but most all would shoot the shorter 39 Sierra well. 1-12" is just barely enough for the Hornady 40, if it's a true 12, it'll shoot like gangbusters, if it's a fuzz slower, not very well at all. The bullet differences are stark, looking at the picture. Longer boattail on the Hornady vs. the Nosler and Sierra, bearing surfaces, etc.
You can roll a turd in peanuts, dip it in chocolate, and it still ain't no damn Baby Ruth.