Is your range covered? The blast from any firearm will reflect off the roof and return to you at a 2x amplitude if covered. Wear good muffs with earplugs. I used to be a IPSC National Range Officer and was subjected to thousands of major Power Factor 38 Super and 45acp blasts from compensated handguns. The noise would leave me with a headache by the end of the day. Those are not even close to the blast from a heavy rifle like your 458. I once shot a 50BMG Barrett Rifle under a covered range with only muffs. The blast from the muzzle brake hit me like a punch in the face and made my vision go white for a few seconds. The recoil was less than a 12ga shotgun since the rifle was about 30lbs. For reference I am not recoil sensitive and find the recoil from the 500g full power ammo in the 458WM out of a 11lb CZ550 to be pleasant and very tolerable. But, once I shot my 375HH at the range and failed to hold it firmly with a good cheek weld. That rifle is about 80% the recoil of the 458. Mild in my view. I had been shooting some 22lr matches and was holding the 375 like an egg. Big mistake. It smacked the hell out of me. Purely from poor shooting form. I fired a second shot and that hurt too. I had a bruise the size of my hand for a month from that error. I know guys hunt ele with 375's but if it was my * I would want your 458 for that job.
Something I would suggest no matter which direction you go. Practice shooting tiny little tgts at closer range with a 22lr off of sticks for several weeks prior to your safari. Also shoot mid-size highpower like a 308 or 30-06 from sticks and limit your exposure to the 458. Ideally, you will find a 22lr and a mid-sized rifle that are closely matched to your 458 in size and feel. I use a CZ452 to match the Mauser pattern rifles or a Winchester 52 Sporter. I also use a custom Sako Quad 22lr in a McMillan A5 stock to match the weight of a heavy gun off sticks. I shoot 1/2" DumDum lollipops stuck in a earth berm in my yard at 35y. The 1/2" tgt at 35y is roughly equal to a 3" tgt at 210y. It is a challenging but makeable shot and it trains you to mount the sticks quickly and precisely the same way each time and to quickly acquire the sight picture and take the shot. 3-5 sec is the par time for such a shot. That is about how long a Kudu will stand still once it is aware of you. I try to be proficient enough to make five DumDum shots in a row without a miss each day leading up to my hunt. It works. I went to the range yesterday with my pair of Safari Rifles for a final range session and shot about eight rounds from each off sticks at a 200y steel plate. All hits, no misses and all the hits from both rifles made a nice pattern about 6" in diameter. The plate was 8"x12" rectangle, and a 2nd was 6" diam round. It is a great confidence booster prior to a Safari. Time to switch on Predator Mode.
For Ele, you will likely shoot offhand at very close range. For that the same approach works. Shoot a golfball sized tgt or plate rack at 30-ish yds with the small bore until it is automatic and then transition to the big bore. That helps you to train without bashing your gourd with recoil and muzzle blast all day, every day. My 2-cents.
