Use a bullet with enough weight and a SD high enough to give adequate penetration on the game hunted. Elk size game need more bullet weight to ensure adequate penetration than deer. Deer size game can be taken with bullets in the 100 gr range easily. I'd place 130 gr as about the minimum for elk, and even heavier bullets for bigger game.
Some of the harder premium bullets need 2000 fps or more to expand, others expand down to 1800 fps, a handful as slow as 1600 fps.
A handful will stay together at speeds over 3000 fps impact, but most give erratic results if they impact over 2800 fps so there is a balancing act. A magnum cartridge will give you a little more range before bullets drop below the minimum speeds needed for expansion, but might blow up at close range with soft bullets. With harder bullets they work up close at high impact speeds, but drop below the 2000 fps threshold at closer ranges.
Find the info you need and run the numbers through a ballistics program. The ranges where the bullets impact speeds vary between 2800 fps down to 1800 fps is the cartridges effective ranges. That doesn't mean the shooter is good enough at that range, but the cartridge is. The results may come as a surprise.
Flat trajectory simply isn't an issue beyond about 300 yards. All cartridges drop enough that exact ranging is critical along with a BDC type scope. That can be calculated regardless of the bullets trajectory.
A 308 loaded with a high BC 175-180 gr will leave the muzzle at 2600 fps and not drop below 1800 fps out to 550 yards. A softer bullet like the ELD-X wouldn't go below 1600 fps until 700 yards. BTW, that is faster than a 170 gr 30-30 bullet impacts at 100 yards. If a 30-30 is a 100 yard cartridge, there is no reason a 308 isn't a 600 yard cartridge.
A 6.5 CM with a 143 ELD-X has enough mass to give adequate penetration on elk, but doesn't drop below 1800 fps until almost 800 yards. Almost 1000 yards before it is below 1600 fps
A 300 WM shooting a 200 gr ELD-X at 2900 fps drops below those speeds at exactly the same ranges as 6.5 CM. But might be going too fast inside 100 yards where impact speeds would be above 2800 fps. And if trajectory is something you think about the 300 only has about 20" less drop at 800 yards. At a 1/2 mile 20" is not much. And a 300 WM won't kill a game animal any deader than the 6.5 CM.
We have to be honest with ourselves. What good does it do to have a rifle capable of taking game at a mile, if we don't have the skills to shoot beyond 1/4 mile. I have owned lots of rifles, including many magnums, but I sold my last 300 WM after buying my 6.5 CM and consider it an upgrade.
I hear your thought process, but the HPBT target bullets aren’t designed to expand at all.
False.
Target bullets aren't designed to take game, but many of them have proven to work well even though not designed to do so. Some exceptionally well, and if they have a shortcoming some expand too much. The Lapua Scenar target bullets have earned a reputation for being an excellent hunting bullet as have several others. But to be fair, some target bullets do not work well on game.
