Here in the lead free portion of CA, we've found, as did Barnes, that the 50gn Varmint Grenades won't work in a 14 twist. Barnes even says so on the box and in the manual. Barnes recommends that they be used in a in a 9 twist or tighter. Save them for your AR. If you check the length of the 50gr Grenade, I think you will find it as long or longer than the 70 gr lead bullets
The 36gr Grenades have not been at all impressive in the slower twist barrels. A 14 twist was only marginally acceptable and the 12 twist in a Howa/Vanguard proved satisfactory though not exceptional. It seems that TAC in the .223 and W748 in the .222 gave the best results.
A final observation. When contact is made with the pesky ground squirrel, the results are deadly but unimpressive. They lack the technicolor of more explosive projectiles and as such limits the joviality of the hunt.
If your required to use lead free ammo, or just want to, we're finding the Speer TNT Green and the Nosler Lead Free Ballistic Tip are giving much better results.