Bases tearing out with the sprue

[ryanmattes]

So in some cases I'm getting a ragged indentation where the sprue is cut. I've searched, and haven't really found anything talking about it. Either it's unusual, or I just don't know how to search right.

It doesn't happen all the time, but enough that I'm not happy about it. Can anyone tell me what this is? Do I need to wait longer before cutting the sprue, so it's cooler/harder? Is it about mould temp?

I just need a place to start to figure out how to fix it.

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[Winger Ed.]

A picture would help, but it sounds like a shrinkage hole.
Lower your pot temp. a bit and see if that helps.

If your casting for handgun boolits, its not really a big deal.
I don't toss them back in the pot just for that.
I save them for more informal shooting. They will still hold to 'one minute of soda pop can'.

[ryanmattes]

It's not very deep, but deep enough that the coating doesn't cover it.

I have a decent-sized button of sprue over every one of them when I cut, usually connected to each other (it's a 6 cavity, so they don't always all connect), so it's not like it's shrinking down into the mould from lack of lead on top, is it?

The one in the picture got by me and I coated it, which made the hole all the more obvious. It looks rough, more like a tear than I would think shrinkage would look.

https://uploads.tapatalk-cdn.com/20201017/5048df1ded65d86d15df77bc54230811.jpg

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[LinotypeIngot]

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

[ryanmattes]

Is that just overall temps too high, or is it something a 10 count before cutting could take care of?

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[Bazoo]

It's from cutting your sprue a few seconds too soon. 5 to 10 seconds I'd say. Backing off the amount of puddle will allow the bullet base to cool enough without any other changes. Or running your alloy a bit cooler will allow the same tempo. Ambient temperature will make a difference in how hot your mould runs too. If it's 50 vs 70 you have to change cadence or temperature slightly.

[Tripplebeards]

Imo It’s your cutting time vs pouring. I’ve cut some nice bases but have smeared lead across my mold in the process by doing so. It’s either from cutting to soon...or to late. I’m guessing to late. The lead starts to harden and takes a chunk with it in my experience. Experiment with your sprue cutting times and take a look at your bases while doing so. You can see the divots in my bases in these and I can stack them in top of each other at 25 yards. I normally run a GC on all my boolits accept for these. A GC will cover up my ocd imperfections and give it a nice even smooth base.

https://i.imgur.com/mxBhbqj.jpg

[Winger Ed.]

Is that just overall temps too high, or is it something a 10 count before cutting could take care of?

You're close. I'd tinker with the heat, cadence/how many seconds before ya cut the sprue a little bit.

It one of those deals like Grandma's gravy, its not an exact science.
Even when it comes out a little different once in awhile-- its still good.:bigsmyl2:

[kevin c]

Lyman 4th ed. Cast Bullet Handbook mentions this. Mike Venturino, who wrote their chapter on casting issues, mentioned two causes: bullet not yet hard enough and a dull edged sprue cutter.

For the first I was told to watch for the sprue puddle to change color, count off three seconds and then cut. I guess you could shorten or lengthen the count as needed, or try other methods like altering alloy temp or slowing the cadence to cool the boolits in the mold faster. For sharpening up the cutting edges I'll let those who have done it speak their piece.

[ryanmattes]

I've only cast about a thousand out of this mould, so the sprue plate shouldn't be dull.

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[Conditor22]

I'm long winded and slow at typing :(

same answer as above. sprue "cutter" can be dull from factory. IF sprue cutter is dull you will get lumps on the bottom of the boolit IF you let the sprue cool to much.


two possible reasons
1) you are cutting the sprue too soon -- wait for the sprue to change color
2) the sprue hole is too shallow/not sharp on the bottom -- has a thick edge on the bottom -- REMOVE SPRUE PLATE FIRST
get a countersink and hone the hole so the cone goes all the way to the bottom
I use https://www.harborfreight.com/50-pc-diamond-rotary-point-set-69665.html
or a countersink bit (if you use a countersink make a cone with wet/dry sandpaper (sand on the outside) to fit the hole stick a Philips screwdriver bit in it or sharpened piece of wood with something stick on it and spin it in eacn sprue hole to smooth them out then then get a piece of glass some 400 wet/dry sandpaper and sand the bottom smooth before putting the sprue plate back on the mold.

I cast with the alloy between 680° and 720° depending on how hard the alloy is (the harder the alloy the lower the temperature need to be) for pure I kick it up to 750°

the hotter the alloy temperature the more the boolits will shrink after you cast them

the bottom of the boolit should be smooth IF everything is correct with a slight discoloration where the sprue hole is

DON'T OVERTIGHTEN THE SPRU PLATE. the spruplate should almost swing freely by itself. I usually add a second wave washer to the sprue screw to help keep a light hold on the sprue.

over tightened sprue screws and/or lack of oil can damage the top of the mold
https://i.imgur.com/K2u3KRO.jpg

I put a little blue 2 synthetic stroke oil/gas mix in a needle tip drooper bottle so I don't put too much oil in the sprue screw ( to much oil will migrate into the nearest cavity and cause problems :(

pre warm the mold on a hotplate (with a sawblade or piece of steel on it) to 400° for good boolits from the first cast

[Tripplebeards]

I casted some more of the above lee 255 grain boolits today. As soon as the excess pour on the sprue turns solid I cut my sprues. I did have a little lead smear on my mold a good couple dozen times but instantly and easily wiped off the lead smears with my gloves. I could have waited another second or two and I’m sure it would have Eliminated all, or most, of my lead smearing.

[la5676]

For my Lee 6 holer 9mm mold, I run the temp fairly high, I kinda like the fill at that temp, but I also have a very damp towel beside me that I keep cooled with additional water all the time. About every third cast I lay the mold on the towel to cool the mold down. Lee even recommends it. I’d get those base tears when the mold gets too hot. Just needs cooling off, but don’t overdo it.

[jsizemore]

Cutting the sprue too soon. The bullet is not cool enough to cut instead of tear the sprue. You might use a timer to figure the time between pour and cut. Makes for consistent bullets too. With my 4 cavity iron molds and an alloy temp of 700degF, my time between last cavity poured and cut is 20 seconds. 4-6 cavity big block aluminum molds are about the same 20 seconds for 200-250 gn bullets, and 18 for 115 - 145 gn. With the mold up to temp, about 400, I get good bullets with a good sprue cut from the start.

[LouB]

Sprue plate "ripping" out the sprue on casting

One other thing to check is the tightness (or lack there of) of the screw holding the plate flat against the mold. Sometimes loosens up a little during a casting session, then when hit , the plate may be slightly lifted as the cut is started.

Don't ask me how I know.
LouB

[Slugster]

I wait until the puddle on the sprue plate has solidified, give a 3 second count, then give the sprue plate a whack with a small dead blow hammer. Sprues will be very uniform. When casting, you want to eliminate as many variables as possible so that your boolits will have more consistency. Work up a cadence in your casting. Also look into a temperature controller if you haven't already. Member HATCH sells an excellent unit.

[BNE]

The only thing I see wrong there, is it is slightly off center. Maybe your sprue plate is not closed all the way?

Otherwise, I try to have a small tear when I am casting. I prefer a small tear over a solidified cut. It is really a cadence thing.

The more consistent you can be, the better.
Pot Temp
Mold Temp
your timing
How much you over pour onto the sprue plate.
How fast do you have the mold filling.

Probably other stuff, but the idea is to make it consistent. I think it was GEARNASHER that taught me this. He said you want to see "Goat butts." Ok, he said it differently, but you get the idea.

BNE

[kevin c]

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.

[GregLaROCHE]

As everyone has already said, temperature of sprue when cutting and/or sprue plate not sharp enough or perfectly flat on bottom or tight enough.

[Hanzy4200]

Cutting the sprue to soon, or maybe a to-loose sprue plate. Just my opinion, but I highly doubt it is going to effect your accuracy in any significant way. For over heated molds, my method is to run two molds simultaneously. 6-7 casts on one, lay her down to rest and pick up the second. It's a stupid obvious method, but one that took me a few years to think of.

[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.

270182
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/thewelder/article/aluminumwelding/aluminum-workshop-a-hotshot-s-guide-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. :D

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?