Lehigh defense makes a bullet called controlled chaos. They claim a minimum opening velocity of 1500fps. Which i have seen tested with the 152g version. Video in post #5. They also make a 175g version.Bullets almost never fail. They do exactly what they are designed to do virtually every time. The problem is when people choose the wrong bullet for the task they are trying to do. Bullets range from soft to hard and there are multiple variations between the 2 extremes.
Softer bullets expand rapidly. They may over expand and give poor penetration if used on larger game shot at close range. They work better on smallish, big game like deer, and since they expand rapidly are a better choice for longer range where bullet impact is slower. If used on bigger game and at closer ranges going to a heavier bullet will slow down impact speeds and improve penetration. Most soft bullets expand well with impact speeds between about 1800-2800 fps.
The bullets on the hard end of the spectrum will stay together and penetrate at any speed you can get from a rifle. But they need to impact at faster speeds or they don't expand at all. You can't shoot them too fast, impact speeds of 3500 fps won't hurt, but if impact speeds are under 2000-2200 fps expansion is poor and they act like FMJ.
It would be a good idea to look at a ballistics chart and look at the projected bullet speeds at various ranges. If using a soft 150 gr bullet it might be fine in a 308 at any range from the muzzle out to about 400 yards. But the same bullet fired from a 300 magnum will overexpand and perform poorly at ranges inside or about 150 yards. But it will retain the minimum 1800 fps at greater ranges.
The solid copper bullets are on the extreme hard end of the spectrum. They work great at close range. Even in cartridges normally considered borderline too small for the game hunted. But because they need to impact faster to expand aren't the best choice for long range hunting.
But you must 1st define long range. They will still retain 2000 fps out to ranges farther than most of us need to be shooting. Especially from magnum rifles.
The barnes lrx supposedly has an opening velocity of around 1600fps. But that was some googling, no direct from barnes.