The only way to guarantee DRT is a CNS hit, ie shot placement. A double lung/heart shot anything with any caliber can oftentimes make 'the run'. There is also bullet construction, impact velocity and its relation to bullet construction, state of the animal at impact, and wound path that determine the duration from impact to death. Shot placement and bullet construction are far more important than bullet diameter in my limited experience. Hard for any animal under 1500 pounds to survive a well placed shot from a 7mm or 30 cal. bullet that is designed for the purpose and delivered within the design parameters. If you get that 7 em em it will not let you down if you do your part. It's always up to the nut behind bolt.This is kinda like a Ford or Chevy question… or more of a F-250 vs 2500 question. The real reason for both is in the name…. Remington or Winchester. They are in the business of selling guns and ammunition. What better way than coming out with a hot new round to sell more guns and ammo? Reference the 30 Nosler, 300 WSM, 300 SAUM etc. are any of them really needed?
I shot a 7mm Mag for years but I was never happy with the way it didn't nail elk on the spot. They just seemed to flinch and walk off and die in "X" number of yards. There are times when that matters. So I bought an 8mm Rem Mag and it is an awesome round. Everything I shot with it from coues deer to elk to caribou to oryx just dropped. I don't care what the 6.5 crowd says (I also have killed a lot of deer with a 6.5 Sweede which begs the question about the need for the 6.5 Creedmoor but we'll save that for another thread) but a bigger/heaver bullet just kills critters faster. An elk "feels" the difference between a 7 mag and a 300 mag. They definitely feel the difference when hit with an 8 mag or a .338. I've witnessed it multiple times.
I would still shoot the Big 8 if not for the lack of factory rounds. It's not that I mind reloading, I actually like it but the last time I went to Alaska I was a nervous wreck worrying about my bullets not arriving with my gun. So I made a visit to my local Wal-Mart, Big R, and Cabelas and looked to see what they stocked – everyone had a huge selection of 300 Win, more than anything but '06. All of that to say, when I replaced the Big 8, I got a 300 win. I know it will kill faster than the 7 mag and I can find factory rounds anywhere in the world if necessary.
Let me add – I am not recoil sensitive. I can't tell the difference between an '06 and a 300 win (I do notice a .338 recoil though and my 416 Rigby rattles my teeth) so that is not a factor for me and I don't believe in overkill or "too dead." Ask anyone who had to pack his buddies "well shot" elk with 270 out of the bottom of a black canyon 200 yards from the mesa top where it was hit.
I never make a rifle purchase based on the disposition of guys that don't like loud guns at a rifle range. Just me, inconsiderate as I am.This can be said about the .270 Weatherby Mag when we have .270win. You only gain around 5% to 7% increase in performance. Brass is hard to find and expensive and you burn up powder a heck of a lot faster. Guys to the right and left at the range don't really appreciate the muzzle blast.
The same could be said about adding the 270 WSM and now the 6.8 Western, but we have them and they're cool. Also, I quit caring about the other guys at the range and my muzzle blast, I just give them a fair warning. I was shooting next to a kid a few weeks ago and told him if it gets too much for him to let me know and I would stop.This can be said about the .270 Weatherby Mag when we have .270win. You only gain around 5% to 7% increase in performance. Brass is hard to find and expensive and you burn up powder a heck of a lot faster. Guys to the right and left at the range don't really appreciate the muzzle blast.