Have you shot it yet???? and what is heavy???? I can tell you where you can get some excellant 700 gr. bullets but even sub-sonic they would be a killer, on both ends, in a Handy Rifle. I think all of the powder manufacture have data for the 500 S&W on their web page, this is data you can trust. You can also check out www.handloads.org, but alot of this data was not presure tested. You should have no problems if you stay with bottom end loads and since your looking for sub-sonic. If you need more data PM me and I`ll PM you some.