1. Mining range lead is harder than you would think, cleaning it, is even harder, especially if you mine 100's of pounds.
2. Rifle casting is different, while .223 is becoming more popular to cast with, don't expect to get a gun to cycle on your first loading, or 5th, or 10th. A Semi-loader for lead has long been thought to be next to impossible to load for, today, people do manage it, but it's not easy. Also, you will likely need a custom mold ($$$$)
3. If you are looking at it from a ROI view, it is a lot like reloading, you won't really save money, but you will shoot more.
4. You will have to worry about casting, sizing, lubing, and loading them. They don't just drop from the mold ready.
Cons:
1. Lubing and sizing can be done with a 20 dollar Lee sizing die. I personally HATE the tumble lube, so I did buy a Luber-sizer.
2. Lubing and sizing is time consuming, unless you have a more expensive unit. The Lee is slow because you have to lube (and then let dry) twice. The Luber-sizer is a little faster, but you are still putting 1 bullet in at a time.