I have a Winchester model 70 in 458 Win Mag and also another in 338 Win Mag.  If I was planning a DG hunt should I add a 375 H&H or 416 Rem mag or would the 338 and 458 be fine?

I haven't done a DG hunt yet but have done plains game. I would think that those two rifles are fine. I wouldn't worry about a .375 H&H.  Are you handloading the 458?

I do not handload,just using off the shelf Winchester Supreme Safari for now

You're good to go. Most PHs will tell you the most important thing is to be comfortable with what you shoot. You could shoot the biggest bore that is made, doesn't mean anything if you don't have good shot placement.  My recommendation is to make a pair of shooting sticks and practice off of them. It will payoff. I made a set for my friend and told him to practice. He of course didn't. Had a hard time adjusting them on the fly to what was comfortable for him.  I practiced in my living room, throwing the gun up on them and adjusting them.   Like I said I was only there for plains game. I'm no expert but I think the .458 would be fine with the right bullet and shot placement.

338 won't be legal for DG in most countries.

Have your 458 reamed to 458lott.

338 good for everything except long range or varmint. Maybe a 308?

Use your 458 as is. You are familiar with it and it will do just fine for you. Your. h will have another rifle to back you up as well. If the DG is buffalo I would run a Barnes TSX up the spout with Barnes solids in he magazine. Elephant just use solids. Leopard and lion you can usually use the 338 in most countries.

You don't need a lot of reach with your heavy rifle  you need reach for bait animals and plains game. Your 338 will l do just fine for thatbPat

Reaming to Lott isn't a back idea. It takes magazine mods and maybe some cuts on the receiver but 458WM has heavily compressed powder and the Lott might only be a shade faster but the powder isn't compressed.

If you can stand the recoil a .458 of either flavor makes a great single gun for everything. 450-550 for DG using iron sights and crank on the scope and shoot 350 TSXs at 2700 for plains game.

If you're looking for a medium the .375HH is hard to beat and any flavor of 416 will do double duty. I'd replace the .338. I don't like them. Vicious recoil, can't fun ammo as readily and not legal or DG. On a DG hunt if I'm going to have a magnum for a second gun it's going to be legal for DG.

Agree that second gun for DG/PG hunt really needs to be legal for DG, hence the 375 is perfect.

 

There are no flies on the 458wm. AA 2230 allows loading the 458wm to 2150fps plus with 500gr bullets out a 24" barrel. 2150fps with a 500grain bullet makes the 458wm performance slightly better than the grandfather of all African smokeless Dangerous game cartridgess, the 450NE 3 1/4". My personal DG loads are 500gr Woodleigh solids at 2135fps, 450gr North Fork Flat Nose solids at 2220fps, and 500gr Woodleigh softs at 2135fps, all using AA 2230. H 4895 is good too, but not as good as AA 2230. I have tested both powders for heat sensitivity and there is no discernlable velocity increase from about 40 degrees F to 95 degrees F. Even when leaving ammo in the sun to cook. My solid loads have provided excellent performance on elephants, cape buffalo and plains game targets of opportunity. The softs have been great on the few animals I have used them on, including zebra.

If you do not hand load and you are elephant hunting, I would suggest having ammo custom loaded for you. Hornaday  458wm ammo is just fine for cape buffalo. I would expect that any appropriate bullet loaded in factory ammo would be fine for cape buffalo.

The two rifles I take on a dangerous game safari including elephant or cape buffalo are a 458wm and a 375H&H.

Both are legal for elephants and cape buffalo, and the 375H&H is versatile enough for everything. Since DG gets top billing, best to have a spare. (And I'm a lefty, so borrowing a rifle in case my DG rifle goes tits up or missing is going to be problematic.) FWIW, the largest game I have killed with my 375H&H is a half ton plus eland, the smallest a 10lb Sharpe's Grybok. Versatile rifle!

Most DG areas have some cover, but not all. Where I have hunted DG there has always been cover, and most plains game shots are under 100yds. A 458wm shoots plenty flat enough for that, and for most opportunities, if that is what is in your hands. All of my DG hunting has been in Zimbabwe, in the Zambezi Valley, on the Escapment, in the Low veld, a couple of other areas.

FWIW, the 9.3x62 is legal for all DG in Zimbabwe, and has proven adequate for elephant. I think of it as something of a 375H&H lite. .366", standard bullet weight of 286grs, standard velocity of about 2260fps, iirc. Lighter weight rifle on average. Lighter recoil. Standard length action. Standard magazine size (not drop box) gives four or five depending on the action. Easy feeding. I bought a 9.3x62 for my son for his first DG safari, hopefully In a couple of years. He is 15 and can handle the recoil.

JPK