I don't think it'll matter too much if you keep to a similar charge weight and work from there.
But your assumption of a lighter bullet = lighter charge isn't necessarily the case. Most data I have suggests the lighter bullet has a heavier charge weight, all other things being equal. For example, with a 77gn bullet and CFE223 powder the suggestion is for around 22.5-24.5gn charge and a 53gn bullet is 27.0-28.5gn charge. I wouldn't go lower than the lowest 53gn suggested powder weight.
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