I have tried to load cast for an AR . Not very successful . I think most " modern " AR barrels have a twist that is much too fast .
I was casting ~ 50 grain bullets . I think , considering the 1-8 or 1-9 twist , a much heavier cast bullet would have a better chance ?
And getting it to cycle the action is another issue .
On the other hand , I load lead bullets in .30 Carbine . Once I learned not to size the bullets to .308" , and started sizing them to .311" to .312" , accuracy greatly improved .
I have not noticed a lead problem , but I have not disassembled the gas " tappet " .
If I do my part , I can hit the steel silhouettes at 100 to 150 yards .
Some of the bullets I have loaded , I got from a friend . They were soft lead , swagged is my guess .
The bullets my cousin and I cast are Lee ~ 120 grain and are mostly wheel weight metal .
Tumble lubed in Lee Liquid Alox & paint thinner . With or without Johnson Paste Wax added to the mix .
God bless
Wyr