On paper, assuming a 42ish grains of powder charge - the difference between a .243 with 100grn bullets at 3000 and the 6.5CM with 140grn bullets at 2700 is 3lbs more of recoil in a 6 pound rifle.

What I did for my 10 year old son was a Tikka T3x SS Lite in .308W cut to 20" and loaded to 2800 with 130 TTSX. That recoils the same as the aforementioned 6.5CM load. As he grows I can transition him to full power loads and a full size stock.

Semper Fi