When going from 224 to 172, I believe if you reduce about 0.020" per pass you will have fair luck. Then of course, inside ream or outside turn is probably required.
There are specialty dies built to reduce diameters/shoulder push back out there, usually by benchrest guys that do a nice job for the wildcatter. With a more simplistic mod such as the 17/223 one would think that the ots bushing dies with say three spaced bushings would be just fine...........just one opinion there...........
One day a guy handed me a set of form dies for he said...........17/223. The RCBS box(40038) says form set for 223 to 17Rem...........has two reducing dies, one neck reamer die, and #17 straight chucking reamer. Never used them, but this has my curiosity perked up a little. Guess always had factory 17 Remington brass handy; odd what you accumulate over the years............