I'm trying to decide b/w 1:7, 1:8, and 1:9. The barrel will have a mid-length gas system. I want to be able to buy cheap and easilsy available ammo for dicking around (is military ammo the cheapest?) mainly at ranges from 25-250 yards. However, I also want to be able to spend the dough on some real nice ammo every now and then and shoot out to maybe 350 yards. Which twist is good for both uses considering a 16" bbl. I've read the ammo oracle and I still can't decide.

I'm a 1:9 fan out to 200 yards, does great with 52-69 grain ammo.  That should do you fine for plinking with cheap/surplus ammo, usually in 55 and 62 grains if you're buying surplus.

200+ yards I like 1:8 twist and 69 grain Black Hills.

You'll probably get a variety of recommendations.

1:7 twist should allow you to shoot the 55 grain as well as some of the 70+ grain ammo that will have better terminal ballistics out at 350yards and beyond.

1:9 twist is probably not going to stabilize the 77 grain stuff as well. Although I've seen some people who've reported good results with this setup.

As far as cheap ammo, Wolf is probably the cheapest, but I won't use it in my rifle. I don't want to risk it  despite that a lot of people claim the new polymer coated stuff doesn't gum up the action. The military stuff (XM193) is fairly inexpensive. It runs somewhere in the ballpark of $180-$200 fo 1000 rounds.

If you're looking for a midlength setup in 1:7 twist check out this group buy. It's currently the only way to get a 16" midlength barrel in 1:7 twist.

www.ar15.com/forums/topic.html?b=7&f=121&t=207911