I've always used about 25gr of Varget under a 55gr Hornady SP (usually without cannelure). It's not an FMJ, but loads are similar.
It works good and is as accurate as I need it to be, but it's fairly expensive. I only used it because I also reload for .308 and it was nice to have just one powder, but now that I'll be loading on a progressive I'm going to move to a ball powder. No idea which one yet, but I'm thinking of trying W748, H335, or 2230 to see what works and meters the best.