I have about 150 Cast Performance 405gr long nose gas checked bullets and wonder if they could soften with time. It seems I read somewhere that this could happen. These are heat treated bullets and I dont know how hard they are. Is this true? I only wonder because I shoot them at 2000fps from my stainless guide gun (pretty painful but fun and devestating on deer) and dont want them to eventually lead my barrel.

On a side note, how much does pressure go down using cast as apposed to lead being theres less friction?

By the way, that pic under my name is the muzzle of my guide with xs ghost ring post on top I took just yesterday. Photography is another hobby. I also have the xs scout scope mount with silver Burris 2-7x and Leupold quick release rings. I love it! I now need a good trigger and im ready to rock!

Well, heat treated bulleys first age harden after treating, then do very gradually soften over time. In my alloy, they cast out right at 14 BHN and heat treat to 30/31 BHN after standing for about a week. I had a few that never got loaded up that were cast about three years ago and when I checked them out, they were still right at 26/27 BHN. Still plenty hard enough.
I don't know what your alloy is composed of, but mine is 10 pounds of wheel weights, one pound of linotype, one-third cup of magnum bird shot (for the arsenic) and a three foot piece of 95/5 percent lead free solder. I use a toaster oven to treat my bullets, which are sized, but not lubed prior to treating. So, if I'm doing bullets for a 45-70, I size them .459", heat treat, quench, then use a .460" sizing die to do the lubing. I think that lubing and sizing the bullets after heat treat affects the treatment causing them to soften sooner. It is said that you can lube and size them right after quenching, but I'm not all that sure. First off, that 14 BHN bullet will be much harder right after quenching so sizing at that point just about has to affect the final result, and two, the much harder bullet puts a strain on the luber/sizer machine.
Anyway, those are my thoughts on the subject.
Paul B.