Hi rickyb,
I'd rather ask why a 1:9 twist on a 223. The 22-250 is a great varmint round. It was designed to shoot up to about 55gr pills. These are very well suited to varmints. A 1:14 is just right for most conventional 55gr pills. So the 1:14 twist suites the pill weight which suites the intended game.
So back to my question - why a 1:9 on a 223? Lets just get some background in here first. In the hunting environment you need to get a clean, fast kill. In the military environment you just need to wound them. Thats why in the military it is a breach of the Geneva convention to use anything other than a FMJ or similar. In the hunting environment we use controlled expansion pills that do heaps of damage.
Compared to a 22-250 the 223 is smaller and has lesser performance characteristics. The 223 is very close to the excellent, old 222 magnum. On that basis the 223 with a fast twist is an excellent varmint round to 300yds.
But what do you do when your nation's military use a 223 as a favoured side arm. Many of those guys are going to ask for thier old side kick to go hunting with and the arms manufacturers obliged. They released 223s with high twist barrels to send heavier pills out to distances where they have much less ME than a hunting round should have.
What we will get now is teh age old arguement about how this guy or that has killed all soughts of huge animals with a 223. They're right. You can, but you can do it better, safer and more consistantly with a round that puts more energy on the target. A high twist 223 was designed by the military as a great military round that wounds things. It was not designed as a great hunting round that kills things quick, clean and consistantly.