Bases tearing out with the sprue

[BNE]

BNE, Are your weights consistent?

I would have thought flat bases to be the most uniform weight wise, with small tear outs (even if small) and sprue stubs being more variable.

Hello Kevin,

Good question, I don't know! I have not weighed them. The vast majority of my casting is for pistol bullets. And the vast majority of my shooting is 25 yards or less. If I do my part, the shots can all touch each other. So if my shots are being affected by a weight discrepancy, I can not detect it. My guns and my ammo (at least for pistols) are more accurate than I am. Now if I were to test these rounds at real distances, then it might make a difference. I hope to test this out in rifle ammo some day.

[John Boy]

Five second pour with mold on an angle to vent air, pour a puddle of melt on top of the sprue plate, depending on bullet size to let the melt harden, then cut the sprue plate. Do it correctly and you can shave with the bullet base

[Lead pot]

Yes to hot and cutting to soon is one for sure.
Hard alloy will tear the hole if it's cut to soon.
A hole in the sprue plate to large will tear the base.
Alloy like 1/20 you seldom will have this problem.
Things you can do to cut this down.
Most factory production moulds have rough plated on the bottom and some even worped
Take the plate off and use some 220 grid wet/dry sand or emory paper and lay the paper on a smooth flat surface like glass or counter top.
Figure 8 the plate on the paper till the whole plate looks like it has high spots removed.
polish the plate using 600 grid.
This will also sharpen the cutting edge.
I cast with a tight plate. The plate needs to be pushed, it will not swing freely by tipping the empty mould.
When the puddle grays I use a 5 count and this gets natural as you go along so you won't count later on.
I cast at 750º and when I see frost starting to show up under the cut sprue I turn the temp down.
Also I don't use over the counter moulds and when I order a mould I specify that I want a small .100" hole and I cast Like John mentioned.
When you cut the sprue put down pressure on the plate.

[kevin c]

John Boy, are you directing the alloy stream to hit the inlet of the sprue plate, or the mold cavity itself? How much of an angle are you talking about?

[GregLaROCHE]

A smaller sprue hole is an interesting idea. It may slow production, but yield nicer bases.

[Lead pot]

Greg,

No I don't see a slow down with the small plate hole. The way I cast I start the pour with the mould on it's side and I use a Lyman or the RCBS ladle and meet the ladle spigot to the mould and while the mould is still at 90º I tilt the ladle starting the pour and then slowly turn the mould up still holding pressure till I see the alloy leaking between the plate and ladle spigot I raise the ladle and let it empty over the sprue hole. This does two things, one is putting pressure on the bullet in the mould filling it and the base is sharp and also the vibration of the alloy hitting the plate hole settles the alloy , sort of like pouring concrete in the form and using a vibrator to settle it getting rid of the agate for a smooth finish.
If you ever noticed the what looks like a gray side on the cast bullet, that happens when you pour the alloy in the mould with the sprue hole up and a fast pour, especially if your one that enlarges the hole in the ladle. That is trapped air causing that gray smear on the bullet side.
In reality. The torn cut on the bullet base I don't see it as an issue except that it is a blemish that don't effect the accuracy.
A slow pour with the mould on it's side and slowly rotating the mould will fill the grooves and you will get a good base.

Attachment 270182
Attachment 270181

[farmerjim]

I would guess that the mold is too hot when you cut the sprues.

+1 Too hot,
slow down, or use 2 molds.

[pastera]

Alloy is within hot short range - Link is for aluminum but it happens with many alloys.
https://www.thefabricator.com/thewel...e-to-hot-short

The alloy is at a brittle stage when you are cutting the sprue so it tears instead of shearing.

Cool for a second or two more and the base will cut clean.

[John Boy]

Kevin, Leadpot explained your question nicely

[Lead pot]

Well talking about casting made me heat up the lead pot. I been wanting to do this using the new .44 DDEPP BACO Mould for the .44-77 Shiloh Farmer.
I want some very hard alloy to test using this design because the base will be groove diameter and the shank below the ogive will be bore diameter so the alloy does not have to have much obturation to seal the gas behind the bullet so I added 1.5 lbs Linotype to a 20 lb pot of 1/16 T/L alloy. I was going to use a mix of 9/1 WW/Lino but I used what I had 1/16 T/L in the pot and just added the Lino. This will be the hardest alloy I ever used for the PP bullets.
We were talking about tearing the sprue cutoff on the base. I expected it to be worse with this hard alloy but you can see the bullets I'm, holding in my hand that the cut is not bad.
Using this hard mix I also turned down the heat to 700º. the high tin mix in the lead takes less heat. Like I mentioned I judge the alloy temp by the way the underside of the sprue frosts. looking at the underside of the sprue you can see the frosting is just starting and and this time I checked the alloy temperature and it was 710º.
Like I mentioned that I start the pour with the mould 90º on it's side and tip the RCBS ladle up slowly to fill the mould and slowly rotating the mould upright holding pressure on the sprue plate then raising the ladle and let it empty over the hole to settle the alloy and reduce shrinkage. The sprue plate is snug enough so it will not swing on it's own weight, I have to push it to close it.
Looking at the top of the sprue you don't see a shrink dimple. If I do I know that the bullet will drop light from the mould. Doing this my bullet variances are less than a grain.
I might just as well put this out also because I see this question asked many times. "How do you clean the stuck lead out of the vent lines?"
Well I use what put that lead there in the first place. I split the mould blocks just enough to see a thin line of light and I slow pour alloy in and let it cool. The two bullets you see in the pile with the fins is what pulls the alloy out of the vent lines.

Now to get busy putting the diapers on these nice bullets.

Kurt

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[GregLaROCHE]

Lead pot.
You cast some nice boolits. I use a bottom pour pot, so I can’t try your method. I do see the logic in it. It’s also a real pressure pour. I tried to pressure pour with my bottom pour pot, but it never really worked out. I do get frustrated with my pot and threaten to plug it and get a ladle. Maybe I should.

[kevin c]

Thank you, John Boy and Lead pot.

Not being familiar with ladle pouring, I got left behind there. Can you use the same technique for each of a multi cavity mold?