hi all. i want to start out doing some small ruck marches soon and build my way up to heavier weight and longer distances. i have my father's rucksack from when he was in the Army, but i'm having difficulties getting started! i pack the ruck with about 20 pounds and it just feels uncomfortable walking with it. it feels like no matter what i do in attempt of adjusting the weight, it all seems to shift to one side or the other? is this a problem with the backpack or am i packing it wrong? i'm putting 40 half pound weights inside of it so that may be a problem with them shifting to one side maybe? any input or tips or warnings would be much appreciated. when i get started, i plan on only doing it once per week, a few days before my sprinting session! thanks!!