Author Topic: Shrinkage and other ills  (Read 745 times)

Alan

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Shrinkage and other ills
« on: October 30, 2016, 04:13:14 AM »
Casting bullets is not my forte, although I've done a fair amount. The specific alloy being used, the alloy temperature, the mold temperature, the rate of pour, and even the mold design (dimensions) can cause shrinkage. And not just dimensional shrinkage (rare), but internal shrinkage (hollowing) which is all too common. All of these factors come into play when machining the mold. Unfortunately, the mold maker seldom knows the exact alloy you're going to use, albeit we all use "about" the same alloy (lead with a small amount of antimony, tin, etc.). And he certainly doesn't know the remaining factors!

If we're buying cast bullets, the aforementioned factors are beyond our control, except to say some precasts shoot well, and others don't. Good or bad, pouring our own can (and does) cause the same issues to appear. The point being, that any issues which do occur with self-casted bullets, may have little to do with the mold and/or casting design.


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Alan

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rsterne

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Re: Shrinkage and other ills
« Reply #1 on: October 30, 2016, 08:38:34 AM »
Good point about the internal flaws (hollows), I suppose that could account for some of the flyers we get.... As to the external shrinkage, that speaks volumes about sizing them afterwards to insure uniformity and control over the finished OD.... I know it's not part of your OP, but I recently read a post from the winner of the last EBR Big Bore shoot (Doug Noble) about sizing, where he insists that slightly UNDER the groove diameter is the place to be.... I haven't tried that yet, but you can bet I will be.... The guy he told to try it did, and the group size shrank to less than half the size, plus it eliminated all the flyers.... It amazes me what a difference 0.001" in diameter can make with a cast bullet....

Bob
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