As stated mold is to cold. I never keep my first few bullets, just dump them in a pan and remelt them. I only use them for heating my mold. I have had those sprue dimples in some of my 45's but at 25 yards it didn't seem to make much difference. They were low power target loads so I don't know what effect they would have in a full load at 50 yards.
This is where the feel for it comes in and it becomes more art than science for me. First day after a long lay off few of my castings seem to come out right in the beginning but by the end of the day I'm back in the groove and subsequent days it's like riding a bike.
Finally got rid of my little camp gas stove and got an electric pot where I can control the heat with a thermostat, much better now. You didn't say what your melting rig is but if you have an electric pot you might have to make a heat adjustment and/or slow down after lead additions. Not a good time to be in a hurry.
If you haven't read it yet this thread might be of interest to you.
http://www.thefiringline.com/forums/...d.php?t=346199