Is it possible to post/ship ammo to Zim a few weeks prior to departure on your safari?
I live in Australia

Not without a great deal of paperwork and only then usually only by surface mail.

Better to take it with you as everyone else does or if you're really worried then ask your outfitter to make sure he has some in camp for you. - That shouldn't be particularly difficult if it's a common calibre. - But only if it's a common calibre.

Needless to say it is not that simple.
I will be holidaying with the wife and three kids in Zambia for three weeks beforehand-cannot cart rifles and ammo with me.
Friend can bring my rifles with him when he joins me but he needs to bring his ammo to.
Calibres 500 Nitro and 9.3x66 Sako!!!!

Really the best thing you can do is consult your outfitter and ask for his suggestions. One option might be for him to hire you a rifle or another would be for him to make sure he buys ammo for your rifles locally. 9.3 might be a problem though.

If you do a search here, I think you'll find someone else asked this question recently and Ganyana name a couple of gunshops in Harare that keeps good stocks of ammo. - You could call them and have them deliver it to you at the airport as you arrive.

Wombat,
Private message sent.