Question 1: How old and how experienced a shooter is your grandson? 2: Is he familiar with heavier recoiling rifles? 3: Do you reload?

The reason I ask these questions is, with that light setup, even with a muzzle brake, that bugger is going to pack one hell of a punch on the butt end! Granted it's more of a "push" than a sharp snapping kick but it's going to still be a pretty good shoving match with that light rifle setup.

The reason for the extra 3 inches is that cartridge absolutely NEEDS at least 25" of barrel to get optimization of burn and pressure release. The best performing .35W I have ever shot or owned had a 26" barrel loaded up with a 250 grain Speer Spitz-SP on top of 53.5gr H335 ( warning , that load is a pretty well compressed load and should only be shot in a VERY strong action rifle) Dang thing printed sub MOA at 100 with that particular load.