I contacted Barnes regarding the loading data for the 50g Varminator and here is what they said.
Do not use the Varmint Grenade data as it would be to weak and that I should use any lead core data supplied by Hodgdon. I found the loading data for the SPR SP in the Hodgdon loading book that listed BL-C (2) with 26 to 28 grains.
I contacted Barnes again (Ryan Farr) for reassurance who told me the BL-C (2) would make an excellent load using between 26 and 28 gr of powder.
I will be making this load this weekend since the Varminator loading data is the same for any lead core bullet.