If you search around, you will find recommendations to stay away from fillers in bottle neck cases; the filler can clog around the bottle neck and cause bad things to happen.
Use one of the "bulk" powders and stay away from fillers in a 30-30.
I always used IMR SR-4759 for my reduced 30-30 loads. Others use Trail Boss.
SR-4759 gets its "bulk" by being a hollow tube shaped granule. Lots of air in there.
The smallest charge or SR-4759 I ever used was 10 gr on a 110 gr bullet.
Don't know how slow it was going, but it dropped more than a 22lr.