Doing A core shot is very time consuming I will give you step-by-step instructions in the pictures below we were using brazing rods cut to the right length for the cavities this method may not work for all molds and of course the brazing rods may be thicker one way or the other depending on the mold that you use after they are cut to length and you get the right size before you place them in the mold you're wanting to oil them so the bodies will slip off the mold that you will see in the pictures is a custom-made one of a kind it is the most expensive mold I ever bought it can't be duplicated.
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Step one placing the rods in the mold getting ready to shoot.
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Step two after shooting pull the pins out of body in replays in mold.
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Step three after replacing the bodies back in the mold you were getting ready to shoot your center color.
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Here is the finished plastic in a core shot.