Tonight I case up 83 .566 Pritchets. I am casting using a Lee 4-20 bottom pour pot, using pure lead. To try and alleviate the cold pin problem, I ran my melt at about 875F. Normally I cast about 750F. I smoked the mold cavities using a BIC lighter, and then I pre-heated the mold on a backpacking white gas stove. I'm casting using the longer core pins.
As is common with hollow-base bullets, nearly all of the bullets have voids forming at the top of the core pin. I tried numerous tricks to prevent this; pouring while holding the mold at an angle, letting the lead impinge on the sprue plate, all to no avail. I suspect the hotter-than-normal lead is part of the issue; the colder bullets I cast yesterday did not have as bad a void problem. Interestingly my heaviest and lightest bullets both have perfect base cavities, telling me there is probably in internal void on the lighter bullet.
Here is what the bullets looked like:
http://imgur.com/yQd3RZ5
http://imgur.com/PxCUB5e
The bullets still tended to stick to the core pins, requiring 7-10 whacks on the handle pivot bolt before they would come free. Towards the end of the casting session they were dropping with 3-5 whacks and I notice that the steel core pins are bluing from the heat. So perhaps the oxidation is making the bullets drop free more easily and the mold is breaking in.
I love the dual-cavity nature of the mold and it greatly speeds production.
I then weighed all the bullets using my RCBS Charge Master 1500. Here are the results:
Weight in Grains.
549.3
551.8
551.8
552.2
553.2
553.8
554.2
554.3
554.4
554.6
554.7
554.8
555.3
565.5
566.6
566.6
567.6
567.7
568.1
568.5
568.7
568.8
569.3
569.4
569.6
569.9
570.1
570.1
570.5
570.5
570.7
570.7
570.8
570.8
570.9
570.9
570.9
571
571
571.1
571.2
571.2
571.2
571.4
571.4
571.4
571.5
571.7
571.7
571.7
571.8
571.8
571.8
571.8
571.8
571.9
571.9
571.9
572.1
572.1
572.2
572.3
572.3
572.3
572.5
572.5
572.5
572.6
572.6
572.8
573
573.3
573.3
573.3
573.4
573.4
573.5
573.5
573.8
574
574.2
574.7
I arrange the values in increasing order as shown. This produces a graph that looks like this:
The up-turn and down-turn portions of the graph are where the weight starts to fall off or increase dramatically from the otherwise linear portion of the graph. So, next I discard all of the data off of the linear portion of the graph and re-graph. That looks like this:
Ideally I'd arrange the data to produce a bell curve, and then I could discard values that fall outside of a standard deviation, but I don't know how to do that. So I just use the linear portion of the graph as indicative of the "average" bullets. The shape of this graph is typical - I generally find that the colder bullets at the beginning of a casting session tend to be lighter than the rest, and as the mold heats up the come up into line. If the mold runs hot you get a few outliers on the top end but most of the outliers are on the bottom end as the mold is heating up.
I then take the average of the linear portion of the graph, and set my maximum and minimum weight limits to be +/- .5% of average. This results in:
571.54 Average
574.4 Max
568.69 Min
5.72 Max-Min
Using this data I re-weighed all the bullets and discarded anything outside the min and max. This resulted in 61 acceptable bullets out of 82, or a discard rate of 25%.
Steve
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