Well, I personally love 30-30s, but since you are looking for maximum expansion, I'd recommend a 44 mag.

Look at the ruger 9644 or 9944. I love my 99-44(ruger deerfield).

Loaded with hornady 240 gr JHP-XTP, you should zero 1" high at 100 yds. You'll only be about 2" low at 150 yds. This ammo will give you the widest wound channel b/c it is already 44 cal going in and then it'll expand to about 1" on impact.

The 44 mag is an often overlooked deer cartridge, but is an excellent choice.