The easiest way to store additional cartridges is to load a similar/base cartridge, make the changes as appropriate(like maximum H20 capacity), and 'SAVE AS' what it is.DAT, in the QuickLoad -DATA directory.
You can open that new cartridge file anytime using FILE -'Load Cartridge Data from File' (there is a buuton for this by the 'Save-As' button.
You should 'Save As' each of your personal cartridge loads, because these will always be unique to your discovery. They are yours, for your barrel.
QuickLoad's default cartridge list is 'qloadfw.vol' which can be opened and edited with a file editor. I use 'Programmer's File Editor(PFE) for Windows, and this is out there for free download. The same applies to bullet, and powder files.
Now, how will you determine the H20 case capacity of an improved case?
I use RCBS.Load 'Cartridge Designer' function for this.
You might enter high confidence loads posted at Reloader's Nest and calibrate your results with case capacity.
The Rifle Section @ www.reloadersnest.com
Keep in mind that the beauty of QL is that you can calibrate it. No other load source is so capable.