5.56 not legal on Red, Sika or fallow. .240 as a bullet calibre is the smallest you can use and 100 gr bullet. (it's different laws in England and Scotland by the way on some of this stuff) so realistically .243 is the typical entry rifle in the UK for all species.
I don't liek .308 Winchester because if its trajectory. It's a fantastically predictable trajectory and superbly accurate - if you know where to aim. The only deer I have ever missed have been with .308 It drops a good bit more than most other rounds.
This could turn into a long thread. Look, energy is the most important thing. This is what kills the deer. Just about every round you can buy will do this (the legal ones I mean) and have loads in reserve. There is a great You Tube link where they take a .22 rim fire out to over 400 yards and it still goes though a half inch of ply and a toasting joint. OK it took them all day to hit the target at that range, but this illustrates my point. They'll all kill, but what you want is point and shoot. If you only shoot over quite short distances then trajectory doesn't matter. Point and shoot. But when your land is very open (err, Africa?) and you are taking long shots then you have to start accounting for the drop. On a roe deer the drop of the bullet can be roughly the same as the height of the chest cavity. You aim in the middle and the bullet will hit the ground not the deer. Please just a note to any closet firearms experts out there, this is a simple explanation to a simple question. So if you want to get into a discussion over ballistics, bog off and have it somewhere else. There's always a smart alec. Now, ALL bullets drop, it's gravity, but you can effectively cheat this by setting the sights slightly high. As you don't generally shoot stuff 10 feet away, you point the bullet up so that it passes through a theoretical zero point (looking down your barrel) at around 180 yards. This is called blank point range. No, not point blank. Blank point. Now when you shoot at more distant targets, say 300 yards, you only have to make up the drop of 120 yards - get it? Now, the curve of the bullet isn't an even arc, it's a parabola. So the bullet drops more and more and more over distance. The .308 typically doesn't fly very efficiently and whilst predictable does drop like a stone. It's ballistic coefficient is about the same as a caravan. And as it's not a very big case, you can't counter that by firing it very fast. I shoot a .300 Win Mag and that uses the same bullet but punts it out much faster, thereby cheating some of that drop. It's fast, flat and hard hitting.
So you can have a small bullet going fast, large bullet going slow or large bullet going fast. Energy is mass x velocity. But it's not energy that's the issue. There is always enough. It's the drop cheating velocity that you are after. Some use a lighter bullet in .308 - I do. This get the speed up which is good actually. But then all you are doing is replicating other cartridges that already do this. For Africa, well firstly what are you going to shoot at? That dictates what you buy I'm afraid and can you actually get it over there to start with? In the main you can but it's all about airlines and customs. Easier to borrow one out there. If it's anything half decent, you will be looking at something like .300 Win as entry calibre and moving onto something like .375 H&H - which you will struggle to get in the UK especially if you are new. I don't think they'd let you shoot much with .308 win. Small antelope maybe. But Khudu, Impala, any kind of Bok? I doubt it.
Chris