I'm also a 20 cal fan, but have had such easy forming & good results with the 20 Tactical that I haven't pursued making a 20 Grendel or 20 Grinch. I've got 20 Tacticals built on Howa Mini & M700, both with Bartlein 1-9tw bbls, and both shoot the Berger 55s accurately, with 3400fps being pretty close to max.
When it comes to heavy bullets in the 22 Grinch, I've not gone beyond Berger 85.5 Hybrids, at 2960fps with MR2000.
When it comes to heavy bullets in the 22 Grinch, I've not gone beyond Berger 85.5 Hybrids, at 2960fps with MR2000.