I've been working with cast bullets in both pistols and rifles for many years now and I've never had any bullet noses ablate off due to heating, and those bullets have a heck of a lot more metplat than a spitzer does. I'm not saying a bit of erosion due to ablation or dust in the air doesn't occur, but the amount is miniscule enough to be of little concern to the average long range shooter. I'm at 1,200 fps to 1,600 fps in my 44 pistol with cast and 2,000 fps in my 375 h@h with cast and both will shoot as well as jacketed or mono bullets in the respective weapons. I hope to get to 2,300 fps with a cast 288 grain 405 slug with my 405 with minute of buckhorn sights accuracy; that'd be a good brush load for mule deer in the badlands.
Lyman has done some odd things over the years and one was a paper patched lead pill in 30 cal that was capable of 3,000 fps out of an '06 sized 30 cal with moa accuracy capabilities (lyman cast bullet handbook page 114); the bullets were making it to the target so I do doubt they were vaporizing on the way there.
The moulds aren't available at this time but from what I've seen over on castboolets there are a couple of specialty makers making moulds specifically for paper patching lead to get good velocity from it.
I've been doing a bit of reading on commonly used lead based alloys and the consensus is that most of them will melt within 100f either way of 600f. With only about 900 degrees on tap to heat with melting a lead bullet to any significant extent will take quite a bit of time. A bit like passing with a car in 5th gear when it's a gutless 4 banger to start with.