The original factory load for the .357 Magnum was basically what you are shooting, but the charge was 15.3 Gr./2400! So 14.0 is well under maximum. Your 12 gr. load is just a bit more than the original .38-44 load for the .38-44 Heavy Duty revolver that pre-dated the original .357 Magnum
My standard N-Frame load is 158 LSWCGC Lyman #358156, LPM primer and the 15.3/2400. Lubricant is Saeco Green. I get very little to no leading with this. I do not shoot this in K-Frame .357s, They will take it, but it really hurts!