My dad and I will be using a 270 win and we will be hunting in either southern missouri or illinois .
I'm pretty sure you won't be using a .270 in IL legally. It is a shotgun only state for hunting unless it has changed since I last lived there.
Here it is from the 09/10 hunting regs.
Legal Firearms
Shotguns, loaded with slugs only, of not
larger than 10 nor smaller than 20 gauge, not
capable of firingmore than 3 consecutive slugs;
or
Single or double barreled muzzleloading rifles
of at least .45 caliber shooting a single projectile
through a barrel of at least sixteen inches in
length; or
Centerfire revolvers or centerfire single-shot
handguns of .30 caliber or larger with a minimum
barrel length of 4 inches.
Legal Ammunition
For shotguns and muzzleloading firearms, the
minimum size of the projectile shall be .44 caliber.
A wad or sleeve is not considered a projectile
or a part of the projectile.
For handguns, a bottleneck centerfire cartridge
of .30 caliber or larger with a case length not exceeding
1.4 inches, or a straight-walled centerfire
cartridge of .30 caliber or larger, both of
which must be available as a factory load with
the published ballistic tables of themanufacturer
showing a capability of at least 500 foot pounds
of energy at the muzzle.Note:There is no case
length limit for straight-walled cartridges.
Non-expanding, military-style full metal jacket
bullets cannot be used to harvest white-tailed
deer; only soft point or expanding bullets (including
copper/ copper-alloy rounds designed
for hunting) are legal ammunition
Well, I guess you could be using a contender in .270.