If you're going to use Varmint Grenades, don't waste your time with the 50grainers.
Instead, use the 36grain Varmint Grenades. The 36gr VG's are as long as a 52gr Amax. I used the Varget load data in the Hornady manual for 40gr Vmax with good success. They are not as spectacular as Vmax but still impressive on little critters.