All good advice everyone.
@AJC1, I'm glad to hear you're using Lil'Gun for heavy bullet Marlin loads. I think it shines there.
All loads were made with the same bottle of Lil'Gun and H110.
All loads were made using CCI-550 primers.
All loads were shot on the same day and in sets of 10 rounds and were shot from a clean fouled barrel.
The gun used was a Marlin .357 Magnum Carbine Levergun.
With a 180gr Hornady XTP bullet Lil'Gun generated an honest 1584 fps
With a 180gr Hornady XTP bullet W296/H110 generated 1495 fps
With a 180gr Cast Performance WFNGC bullet Lil'Gun delivered 1657 fps
With a 180gr Cast Performance WFNGC bullet W296/H110 generated 1547 fps
Unfortunately at the time I didn't have any 2400 to add to the comparison.