I never had an issue with the 243's or the 6mm Rem capability to quickly dispatch a deer from a wide range of angles. Did feel the velocity was a bit more than I cared for in terms of leaving behind more blood-shot meat than I may prefer. I have been using a bolt action 6.5 Grendel for the last 4 years to fine effect.
A Ruger American Ranch Rifle in 6.5 Grendel would probably make a great little rifle to start a youngster out with for deer hunting. An AR-15 in that caliber would work great too with a collapsible stock to adjust for their short length of pull.
