There have been a lot of different comments over the course of this thread, and I will chime in with my thinking on a lot of these issues... FWIW. I didn’t mean to write an essay, but I still seem to have done!
Best 300... I have hunted a lot with a custom Rem 700 in 308 Baer (one of many improved 300 Wby style cases available). The rifle has performed very well for me, but I chambered the rifle originally with my match reamer and got sick of turning case necks for a tight neck chamber, so recently rechambered to a 300 RUM. I would recommend either a 300 Win Mag or a 300 RUM, depending on what the shooter felt most comfortable with. Out to 800 or so yards, there is no doubt the 300 WM will do the job, though personally I lean towards the 300 RUM. Either of these cartridges with a 1/10” twist barrel, in a well made rifle, will cover a LOT of hunting situations.
is one of the more contentious issues in our sport, and there are a lot of people that strongly advocate against them. I dont get that argument, and am strongly in the camp of using a brake. I hunt with hearing protection, and much prefer the precision I can get from a braked rifle (the brake allows me to shoot the rifle more accurately, I’m not suggesting the brake makes the rifle more accurate). As to which brake, in my opinion we have seen innovation in brakes, much like we have seen innovation in many other areas of the shooting sports. In my view, radial brakes like the Vais simply represent an earlier generation. What I consider to be second generation brakes are better at reducing recoil, and also directing the muzzle gasses in ways that avoid blowing dirt & debris all over when shooting from prone, etc while improving further on the task of actual recoil reduction. I have personally used a few Defensive Edge brakes and have no problem recommending them. I currently have an Allen Precision brake coming and have high hopes for that based on what I see in the design. I use screw on brakes, but only screw them off to clean the barrel, or to make transporting a long barrel rifle easier. I agree that brakes are generally not too aesthetically pleasing, but then my long range hunting rifles are not likely to excite many rifle “purists” anyway.
On the issue of brake during guided hunts, it is true that guides may not like them. But it is also true that guides like clients that can hit what they are aiming at. Most guides in my experience (which is mainly limited to African hunting) will accommodate a client with a brake, and many guides now carry some form of hearing protection. I dont believe this factor is a key decision criteria on how you configure your rifle, however I DO recommend you add it to your list of questions for selecting a prospective outfitter.
Also on the topic of selecting a hunt, there are several points that are implied in your rifle selection questions that you should consider when making your choice of a hunting destination. In many parts of Africa, guides consider 100 yards to be a long shot – and are very uncomfortable even considering a shot beyond 200 yards. So you need to discuss your expectations in detail before you book a hunt, just like you do with other factors like the species and trophy quality of game you expect to see on your hunt. The other factor is the type of terrain you will be hunting, as the cover may make any type of long shot impossible. The greatest exception to shooting further than 100 or so yards that I have found in Africa is Namibia, where there is a lot more open country and guides are more likely to view 200 or even 300 yards as being acceptable or even necessary. In other parts of Africa, the cover is so dense, that shots are very short by necessity. On the average, African guides are used to clients that make great claims about their marksmanship, but on the average, these claims are not backed up in the field.
When selecting your hunt, you would be well served to confirm in advance that: you will be hunting in country that allows shots out to the range you are expecting; that the guide will accept that it is ok to take a shot out to whatever you (the client) considers an acceptable range for a shot, and that they will not have any issue with the type of equipment and hunting style you are planning to apply. Then, once on the ground, you will need to show your guide that you can actually shoot as well as you say. Once your guide is confident in your abilities, they will generally work hard to find you the type of shots you are looking for.
On the issue of the risk of losing ammo... where to begin. Firstly, I must say that it can happen. I have made 5 hunting trips to Africa, and hunted with a wildcat cartridge on 2 of these trips. I have not had a problem losing ammo on these trips, but that is due to luck more than anything else as I have had a couple of close calls. I have once had my rifle fail to arrive with my baggage (fortunately on my return home). And once travelling with a friend, our rifles arrived ok, but my friend’s bag had been off loaded before takeoff on an African domestic flight due to an over-loaded plane. In this case I was lucky since I was shooting my 308 Baer, so if my bag/ammo didnt arrive, there was zero chance of finding any locally, whereas my friend was using a 300 WM and was able to get ammo some from our guide. All that said, if you have painstakingly worked up a load for your factory chambering so you can hunt to any distance you are comfortable with, the loss of your ammo and replacement with a factory round will still derail your plans to a large extent. It is very unlikely you will find high BC, precision loaded ammo in camp or in town, so you will be shooting at much reduced distances to what you originally had in mind. Many camps will have a back-up rifle and ammo in camp, and you will probably be equally constrained with this combo. So in my view at least, you are not really at any greater or lesser risk than travelling with obscure ammo than common ammo in many cases.