I was just looking at the same thing this morning. The least expensive bullets and powder I found were at Hi-Tech Ammo. Although primers can be had elsewhere for a little less, the HazMat and one shipping charge make it economical to buy the whole package at one place in this case.
55gr FMJ $65/1000
WC844 $88/8lb
CCI SR Primers $23/1000
LC Brass $65/1000
This comes out to about $0.22 per round with shipping. The second loading will be even cheaper since you already have the brass. I see Midway has Brown Bear for $0.29 per round without shipping. Yes, you will save money and at this price have equivalent ammo. For another nickel or dime per round you can have near match quality ammo using a better bullet.
I tried cast 223 in a 1:9 AR without much success. After hundreds of rounds of testing with a Lyman 55gr mold with different alloys, powders, gas checks, lubes, etc etc the best I could do was the occasional 1-1/2" - 2" group at 100 yards. More common was 3"-6". If one of your rifles is a slower twist like 1:12 you might have more success. I never had any leading whatsoever despite loading as fast as 2800 fps. I did find that the best accuracy in my gun was in the 1700-2000 fps range which was on the ragged edge for cycling the action.
