I've just started casting and while using the same alloy with the 312-155 mold I'm getting weights ranging from 60.5gr to 65.1gr the first melt most were in the 61 +/- .5 gr and the second melt the only change is that I was water dropping them and most were 62 +/- .5. I've been sending any out of the stated ranges back to the pot along with any with visible blemishes. Am I having a problem or being to critical?