Originally Posted by
JonB_in_Glencoe
This is excellent advice.
You'll be able to answer most of your questions just by reading the first half of the manual. Then you'll have a grasp of what to ask and what specifications need to be provided so others can answer your "advanced" questions.
But, I'll offer you a few quick answers for "If i want to lob some 550gr at 1050 or less".
For a marlin levergun, the alloy doesn't really matter, except softer is better, but you could use 18 Bhn hardball with no problems if you get a mold that drops a large enough boolit. You probably want something like .460" Lee molds tend to drop closer to .457 so that is a reason to swing for a NOE mold, or other brand that'll likely cast that large.