If you push cast GCed rifle bullets too hard, leading can occur very quickly and totally destroy accuracy within just a few shots.
I find I can get low to mid 2k fps, before I get any hint of leading.
I use the hardest alloy I've got and I make my own hard lube, so it's not just blown off by the higher rifle pressures. Then I also tumble lube them for extra assurance.
This sounds like it's alot of effort, but I enjoy making and shooting my own made bullets. And the price of factory produced jacketed bullets these days, makes it more worthwhile.
Gaschecks, lots of lube, hard lead and not too much velocity will keep your barrel unleaded, which is always a good thing. IMO