White box simply means factory ammo. The DE has far more weight than a revolver and handles factory better. I also use cast without gas checks without issue but keep the velocities down. If you cast harder bullets or quench them as they come out of the mould they come out harder and it will raise the Brinell hardness in them. Your lube also depends on how fast you push them. You specifically said you'd be using recovered lead from the range, so you'll have some really good stuff and some wheel weights I would think. If you collect a good mass before melting and casting you can likely get a good mix. Like you say, you'll have no real idea...then you need to flux it with bee's wax to keep the tin down in it...don't get the mould too hot or you get frosty bullets, too cold and they're wormy. Read Lyman's cast bullets and you'll see.

One last thing about the DE, I think they suggested no lead as it has a gas port and polygon rifling, two things they thought would give trouble with lead. I had no problems with either. There's lots of variables with cast though...