I have had a number of 12-14T 6 BR's.
P. dog, ground squirrels, jack rabbits with 60g Sierra, 70g tnt, 70g ballistic tips, and 70g sierra Blitz kings.
My friend, Gene Harwood sat a NBRSA World record in the late 80's with his Heavy Varmint rig shooting a 14T with his own 60g bullets with H335. Later on, I took him shooting squirrels and he chewed me out for shooting H322 with 60g Sierra's.
Two weeks later I was trying H335 with Rem 7 1/2 primers with 60g Sierra's and groups were so amall it was amazing. Another issue with the H335 was how clean it burned at the top end pressures where it was so accurate. I got 8000 rounds out of that barrel an only pulled the barrel because it was starting to copper, accuracy was still there.
For ground hogs there are a couple of considerations. ON my current Lilja 12T, zero freebore chamber, I shoot the 55g Nosler at 3890 fps where it is the most accurate. The 6mm 55g has a better BC than the 22 caliber counter part....like shooting a 220 Swift. The 58g V max is unbelievably accurate, so is the 65g V max with awesome velocity. The 70g is still very, very accurate but not as fast so the trajectory is no where near as flat, with the 70g Sierra Blitz king being the most accurate of the 70g weight out of my 12 twist.
At 300, the nosler 55's are shooting from 3/4"-1.25" groups, depending on how much wind there is on that particular day with H335 or AA2230.