Once you have decided on a load and your rifle is sighted in stop shooting off the bench and just practice off the sticks. I did most of my shooting stick practice with the a 22 and was shooting very well. When I started shooting my 35 Whelen off of the sticks my group opened up dramatically. My father and brother experienced the exact same issue but we where all able to improve our shooting with our hunting rifles before we left for Africa. You have plenty of time before your hunt so start with the 22 but 6-8 month before you safari switch to your hunting rifle and you'll be fine.