Congrats to your boy, that is GREAT!
Get him the biggest rifle he can shoot accurately and load it with premium bullets. Make sure he knows that you need to shoot an Oryx thru the shoulder to get the good stuff, guts are way forward.
The numbers are not what they used to be 10 years ago. Success rates have dropped but it will still be a great hunt. Stallion has a great number of huntable animals. Get on a high spot looking west first thing in the morning. WHen the sun first comes up it makes them shine like a new penny and they are much easier to see.
Take two sharp knives.
Most of the Range cops and Game wardens are good about helping the kids find animals, let them know.
Don't take cameras, they are fussy about that.
You guys are going to have a great time.
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