Mould problem

[Blackwater]

I've got a Saeco #745 mould for my .45/70 BPCR 1885 Browning. It's a 533 gr. sort'a semi-pointed Creedmoor type bullet with a small flat point. I've always gotten good bullets from Saeco moulds, and this was my first casting experince for a really heavy bullet.

The first time I cast with it, I used WW's with @ 2% tin added in the form of 50/50 solder. Got spunky and cast some 350 or so. 70% of them were @ 15 gr. light, and had voids in the base. THAT was a BIG disappointment, and I subsequently remelted them and gave the lead another chance in another mould. The alloy cast fine in another, lighter pistol bullet mould, so it wasn't necessarily the alloy.

I'd read where many big bullet BPCR casters recommended using only plain lead/tin alloys to get the best and most consistent bullets, so tried that, using @ 30:1 lead/tin. These bullets came out just fine, and gave me something I could use effectively in the BPCR.

I guess I really have two questions here. One, what is it about the antimonial alloy that made the bullets get a void with that alloy, while the lead/tin alloy did well; and Two, would enlarging the sprue hole in the mould likely let it cast void-free bullets with WW's, and if so, what would be the effect on the plain lead/tin alloy casting? Any cure recommendations would be appreciated.

BTW, it's a 2-cav. mould. They didn't have a single cavity when I ordered, so I got the 2-cav version. Thanks for any help here. I AM learning!

[45 2.1]

Nothing wrong with the lead, it was the technique that got you. When you try it again, adjust your temperature until the sprue takes about 5 to 6 seconds to freeze. Wait the same time until you cut the sprue also. The alloy will be at the right temperature then, though you might have to cast more slowly to keep from overheating your mold. Slow and easy does it.

[waksupi]

Blackwater, turn up your temperature of the pot. Way, way up. I bet you will see much closer weights, then.

[Buckshot]

...........Try the "Standing Wave" technique (thanks to Precision Shooting magazine). When using a bottom pour for big boolits, it works well. As a cavity comes full via a stream of alloy you can see it 'bounce' a bit up out of the spreu hole. Continue to allow the lead to flow another 1/2 second. Then go to the 2nd cavity and do the same. Angle the blocks down a bit and put an ingot mould on the base of the furnace to catch the overflow.

Let the sprue puddle sit a couple seconds past the turning point and then strike it over. You should see perfect bases.

Boolits cool from the bottom (nose) up, and the outside in. Stands to reason as those are the areas in contact with the molten lead and that's where the heat goes. Into the blocks. The cooling alloy shrinks a bit as it cools and pulls the still molten alloy down toward the nose and at the same time out toward the OD.

You generally do not see voids in the nose half of the slug as it's cooling and drawing lead from that still being poured into the cavity. As you fill up toward the base near, and then finally TO the underside of the sprueplate 2 things happen.

1) The molten lead avail to draw from has shrunk to the area of the hole in the sprueplate.
2) A new heatsink area in the form of the spruepate itself has just created a much larger area for heat to escape into, right there at the base of the boolit.

By allowing the hot alloy to flow a bit longer maintains a hot fluid supply sufficient to make up for alloy pulled out of the center via the OD of the boolit.

................Buckshot