dnovo,
You may want to look up some of Ross Seyfried's old articles in past issues of "Handloader" or "Rifle". His formula is 40-45% of the original black powder weight in IMR or H-4198 and as much dacron as you can stuff in the case under the bullet. In my double I use 69 gr of 4198 and 17 gr of dacron under a 610 gr bullet from a NEI mould. I have found that I need to use mag primers in 577 cases to get reliable ignition. Be sure to use plenty of dacron, too little can lead to chamber ringing. The cheap pillow stuffing from wally-world works as well as any.
Hope this helps.