I empathize with you in keeping the Spousal Unit happy in her shooting. My wife is a petite gal who plays piano professionally and her hands won't tolerate anything close to what I shoot regularly. I am ham handed and can shoot a HOT 45 Colt load all day. One of these is far more than she can tolerate in her hand, wrist, or arm and I won't subject my lady to any abuse that would drive her away from this hobby.
I seem to remember (research powder coating at castboolits.gunloads.com) that powder coating adds about 0.001" to 0.0015" to the boolit diameter on the first coat. If that isn't enough, you may have to powder coat them a second time.
It is best to push one of those bare lubed cast boolits through the barrel with a wooden dowel and hammer. If it achieves none to light resistance going through, that boolit is too small and will deposit lead along the barrel when fired. You are trying to achieve a tight and thoroughly resistant fit when slugging a barrel so the barrel's tightest land and groove is "mapped" on the diameter of the boolit.
After pounding the slug through measure it's diameter, WRITE THAT DOWN for posterity, and KEEP that slug for future reference.
With that slugged dimension, you try to purchase, or cast, or powder coat boolit diameter to fit in the range of 0.0015" to 0.0025" WIDER than the slug (barrel) diameter, but not so hard as to wildly exceed the theoretical pressure needed to mold the boolit base to the lands and grooves on powder ignition.
This wider and softer fit will allow for the boolit base to OBTURATE (get fat) and seal itself against the lands and grooves as it is deformed by the searing heat and explosive powder expansion at primer ignition. If what you have is a hard cast boolit, or one that is too thin along its diameter, it won't obturate against the lands and grooves. Escaping hot gas will melt a portion of the boolit base and lead will deposit along the barrel length (i.e. leading).
Here's a reference for obturation and BHN (hardness) of cast boolits: http://www.lasc.us/FryxellCBAlloyObturation.htm
I suspect your boolits are HARD CAST. As such, they won't expand at the acceleration of the reduced charge, which gas cuts the bases, and leads the barrel. If so, you might research how to soften them.