At high velocity even with lubricant added it can melt in the rifling causing your rifling to clog and making cleaning difficult. Accuracy will also suffering. This is why it is necessary to use a gas check when shooting higher velocities with cast bullets. It you plan to shoot 3000fps a jacketed bullet is necessary. I would venture a guess that at any speed above 1800fps a jacketed bullet should be utilized.
when first starting into re-loading my brother in-law and I loaded some hard-cast(with gas checks) 45-70 gov. at about 2150fps. The lead fouling was rediculous. took a full hour and 1/2 to clean that sucker after about 15 shots (or so he tells me).
THis suprises me that some are seeing hard cast bullets with gas checks and getting lead fouling problems. I have for years used "QUALITY" hard case bullets from Cast Performance with gas checks in big bore rifles at velocities up to 2100 fps but usually around 1900 to 2000 fps. In fact my "North American" 458 Lott load uses a CP 440 gr loaded to 2000 fps and I have never had a problem.
I have seen some cast bullets that were to soft and with poorly fitted gas checks cause some problems.
I believe the question is asking about lead tips on jacketed bullets and what happens to these bullets in flight, not in the bore.
Most of us have seen high speed video of bullets in flight going through something like an apple or something like that. One I remember was a soft point out of a 223 Rem. I believe it was a Hornady 55 gr SP loaded to 3200 fps and just before it impacted the apple, it was clear that there was still a perfectly shaped lead tip on the bullet.
All lead bullets should not be used at 3000 fps for one simple reason, the metal used in these bullets does not have the integrity to hold the lands of the rifling without shearing off. That is why rifles designed for lead bullets will generally have much deeper grooves in the rifling so the bullets will hold the lands better. Modern high performance rifle bores have relatively shallow grooves as the copper alloy jackets will hold the lands much better and do not need the deeper rifling.