Mine actually has an inch or so between the shot and the top of the reservoir (these aren't "bottles") when a bag of shot is dumped in. You could have some left in it and 25 pounds would still fit.
Years ago, I tried a two-liter soda bottle. They make quite a mess when - not if - they collapse. Funny, they only do that when they're full...
Yes, you still have to tip the charge bar assembly to change bars or bushings if there is any powder or shot in the reservoirs. You also have to tip it back to get all the shot out of the reservoir as the drain is a little above the bottom of the aluminum housing. The shot in the bar and a little more won't drain unless it is tilted back.
For the shooter who loads his/her shells a flat at a time as I do, it's nice not having to do anything to the loader after you start loading. The new-style MEC primer tray will accomodate 250 primers, a shot bottle on the powder side holds more than enough powder and Lou's shot reservoir takes care of the lead for 250 shells.
Thanks for the comment, Buc. Here's another view.
Ed