My kid just turned nine, weighs about 65lbs. Very recoil sensitive too, the 410 has brought tears both times trying (attempts at age 6 & 8). With him going to be hunting next fall, it's time to torque up the Grendel a bit. I likely won't let him shoot beyond 125 yards in the field, so my plan was to make a reduced load with enough oomph to be in the impact ballpark of the legendary 30-30, which shoots a 150gr bullet at about real world 2300 fps MV. Due to it's piss poor ballistic shape of the flat nosed bullets (BC .220), that lands at 125Y with approx 1880 fps / 1175 ft-lbs energy
In the Grendel, I'm loading 123 grain Hornady SST over 22.0grs D8208BR. This makes 2180 fps at the muzzle, and at 125 yards it should have 1985 fps / 1075 ft-lbs energy
Recoil in 8lb rifle :
[*=1]Grendel 123gr @ 2180 fps = 5.5 ft lbs recoil
[*=1]243 Win H4895 60% 80gr @ 2700 fps = 4.9 ft lbs recoil
[*=1]350 Legend 165gr @ 2100 fps (H110 24.3grs starting load) = 8.4 ft lbs recoil
[*=1]223 Rem 45gr TSX @ 3200 fps (with starting load 25.0grs H4895) = 2.7 ft lbs recoil
Click pic for video
