You don't need that hard of a lead for handgun rounds. I use lead around 10bhn for 9, 40 and 45. I cast my boolits out of range scrap. Check your local scrap yards for lead also castboolits.com has people that sell lead around $1 per pound shipped.
I cast for everything I shoot. But I do not shoot a 223. That said for the price of bulk bullets I could not justifi casting for such a small caliber. I do cast for 300 blk as the cost savings are huge.
Not likely a fuel issues as it run above idle. Check for a vacuum leak as this will give a rough idle and cause stalling. Also your idle air control motor can cause this issue. Do you have a check engine light on? When below 1k rpm what happens? Any smoke out of the exaust?