One lesson in life that I've learnt is don't cheap out on casters.
My SVT ATA case doesn't have casters so I use a dolly. When loading I get help lifting the ATA case, then I lift the dolly. It is better to have it attached though. Otherwise the case can slip off the dolly. So that is one option.
Don't know if these
are lighter than what you have but they are typical of the industry standard.
There are magnesium and aluminum casters. Magnesium tends to be lighter.