All my varmint rigs are Rem 700 in .223, 22-250 and .243. And oh yeah...... a tricked out 10/22 using Winch. Xpert HP for shooting rock chucks under 75 yards and with good bullet placement one shot can anchor them.
I shoot mostly rock chucks here in Idaho but do get over to Colorado for some PD shooting later in the year. The rock chucks can get up to twice the size of the PD which gives them more body weight to absorb the energy and for back-flips.
Lately about 80% of my rockchuckin' has been with a suppressed .223 pushing 40g NBT at 3900fps and that is a great combination.........when there is no wind and the shots are this size of about 350 yards. I used to bang on them with the 22-250 pushing 50g NBT at 3800 fps but there is an element of fun of shooting them with a suppressed rifle. The 22-250 action usually accounts for about 10-15% of the shooting. There has been times when the ranges were longer and the wind was up and I would use the .243 pushing 55g NBT at 4050 fps but later I moved up to the 70g NBT around 3700fps.
Shooting the .243 was limited as far the number of shots and worked out great for those limited runs. A wee bit more recoil and blast but it is only a .243.
Sounds like your buddy has a similar approach and my guess is the .243 caliber would be a solution and I would recommend the 70g NBT.
We usually don't have the volume of shooting with rockchucks but we do have some locations in Southern Idaho where my buddy and I both use two rifles and with taking turns with those 4 rifles to keep the barrels from heating up.
