I cant see any issue with 20 ton.. in fact I'm sure 12 ton would do er. ROUGH math, the pressure for BLANKING a holster is about 12 ton. But this is figuring a blank that is 24" long and 12" wide, which you'd think would be enough, and that's in 8 ounce leather. BUT, you aren't blanking, you're SLICING, which reduces pressure by about 6x, if the die is sharp.
Seriously, only way you'd ever deflect that sucka is to bottom out the die and continue pressing. Well, the die not sitting straight, but i'm assuming you'd check that.