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The finished product manufactures very smooth, even shot (if you discount the 'sprue' trails)
I made this 20 years ago to provide smaller, yet dense ammo for my slingshots. It has turned out literally thousands over the years……
Being nice and true, they fly true
Rectangle Wood Cutting mat Font Pattern

Rectangle Gas Metal Font Fashion accessory


This can obviously be adapted to make larger diameters, bear in mind that you would need to step up material dimensions if you wished to maintain the production rate

I started with two sections of aluminium block, dimensions 70mm x 60mm x 18mm
(2 3/8" x 2 ¾" x ¾")
The next process was to clamp the two pieces face to face and inline in a firm pillar drill vice, then drill two blind 'pour' holes (please note, blind holes are ones that do not penetrate all the way through the material!) Carefully gauge where the holes are to stop!
Without unclamping, countersink the two open ends of the pour holes so that pouring molten lead is eased.
I then took 7.0mm steel ball bearings (six in number) and then, separating the two pieces of aluminium.
I then carefully measured and marked the positions for the ball bearings on the pour holes on both sides being very careful to make both side markings the same.
I then 'popped' the marks into place with a heavy centre punch.
I then asked a local small engineering shop for a shot of their 100 tonne hydraulic press! (ask about, you can find them!)
I placed the first piece of aluminium on a heavy plate in the base of the press, put the balls into the pop marks, placed the other bit of aluminium on top in an aligned ball bearing sandwich and gave the machine some grunt sufficient to close the gap between the two bits of ali….

After releasing the sandwich from the press (it was pretty much fused together in a block) I took it home & drilled out & countersunk the dowel holes (these are use to correctly align such things as moulds)
I then warmed the sandwich up a wee bit with a gas blowlamp, it fell to bits no bother, this due to the different coefficient of expansion between steel & ali.
Dowels (made from brass set screws) were inserted and held securely in place by distorting the edges of the countersunk dowel holes with chisel dinks.
The pour holes were cleared out by running the same size drill bit back down them.
When cast, the 'shot' comes from the mould like a necklace, I use a fine pair of side cutters to true them, and stored in a bag or pocket, all rough edges on the shot quickly disappear.

Job done.
 

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I need a mold like that, nice work!
 
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