Need a .243?
Yesss, you do. Anna .25/06, anna .270, anna .35 Whelen. But, first things first.
Is a .243 Winchester overbore? Probably.....with IMR 3031. With 4350 or 4831(there are several "models") the cartridge is just fine.(You're going to be a reloader, right?)
If someone is telling you that a .243 is overbore, they MAY be talking about a different cartridge, a .243 Rockchucker, or Super Rockchucker, maybe. Not ALL .243s are the same. Since you're probably NOT a reloader, the .243 Winchester is what we're discussing. It will last about 5000rounds, unless you shoot 'em all at once as a Prairie Dog shooter might if they bring enough ammo with them on a Safari. Shooting 2000+ in a week will burn a barrel, but figure the time shooting versus the time available and that's hard to do in a week. The targets are there, but your partner wants you to spot for him/her, too.
A .243 will last two lifetimes, unless you do a LOT of shooting, which you COULD end up doing, once you get one.
My personal choice is a .25 caliber that I've carried for over 20 years, and USED it, too. Look at the headstamp on my shells and you will see ".243 Win" written so there can't be a lot of difference.
The .243 is common enough to be easy to find ammo. It's light-recoiled enough to be easy to shoot, even in a Featherweight. It's accurate enough to make you shoot more, so you start reloading. It's just fun...Yes, you NEED one.
Have fun,
Gene