Advice from an old Troll... load a ruck like you would for the field, and to the weight you would need for say 5 days living. You'll learn how to pack what you need where you need it. Use gear not sandbags - learn how your ruck balances when you have mission stack, not weight plates in it. What's your basic load of ammo going to be - you'll have min 6x30rd rifle in your pouches, 1x30rd in your weapon, side arm and 4x pistol mags... so figure crew served issue, extra personal (side and long) of 3-400, extra water, rations, snivel gear, commo gear, clothing.... It's better to get good at carrying what you need, getting it in and out of your ruck (at night, no lights) than just humping the weight.
Weight plates close to your back in the radio pouch, with fluffy stuffing is miles from your D-gear stowed for action. Practice stops where you have to get stuff out and repack in short intervals... your ruck is your home, not just a big tick... Learn how to dump your ruck when you need to, and get it back in order.
A geared out ruck takes on a life of it's own, and it carries differently than a "pt" ruck - it was SOP for us to only carry geared out rucks for our marching days... and I'm glad we did.