You might want to buy some .440s and some .445s for a trial. Those Italian guns might not be true .45s .440s might work better.
My son's (and now soon to be my grandson's) little .45 kids rifle I built from an old CVA Kentucky rifle (shortened the barrel and made a maple half stocked for it) performs great with a .017 pillow ticking patch and .437 round ball with loads of 20, 30, and 40 grains of 3fg Goex. I had my son start out with light loads and as he grew older and became effieicent at loading I then would up the charge and ball size to .440, though the .437 worked so well he just stayed with those. Now the barrel on this rifle was shortened from 33 inches to 26 inches and it has a 1 in 66 twist with .008 depth rifling.
Just throwing this out here as I believe the best route is to test different ball sizes, patch, and charges, to see what works best for a particular rifle and what it will be used for. This little kids rifle was never intended to be anything other then a kids shoot rifle a Rendezvous and it sure proved itself in my son's hands.
