The Country Boy was not a magnum rifle. In fact I think they were restricted to 100 grains of powder. But I do not see how moving from the #11 to the 209 ignition would hurt the rifle. Your just putting more fire into the charge is all. The ignition itself adds very little to the over all barrel pressures I would think. But I am a strong believer in not changing the design of a rifle unless your 100% sure of the safety issues. On that I can not comment as I have no background in that area.