Preventing base tear out.

Make sure the contact surface of the sprue plat is clean and sharp. I run it across a stone to make sure there are not any burrs.

I find that when the mold is getting too hot and I move the sprue plate I get base tare out. The cast bullet is not cool enough.

You could just wait a little longer before moving the sprue plate.

I set the "hot" mold aside and cast a different bullet. Untill that mold is too hot.

Its probably from cutting the sprue a little too soon. I have rubbed the bottom of the sprue plate on a hard stone or on a piece of emory cloth on a piece of steel plate.

As the lead cools, it seems to go through a brittle stage where it fractures instead of cuts. Let the mold cool a bit more before cutting the sprue plate.

Interesting. My observations are:
Too soon and the lead is still too hot. This results in smears.
A little later, the lead seems brittle and it fractures as it is not totally 'set' yet.
A little later and a little cooler, the lead seems to cut better and rather easy.
Wait too long and the lead cools way down and starts to harden and it is difficult to cut.

I have the same problems with tearout. If I had a six bullet mold I wouldn't get so impatient on hitting the sprue cutter to early.
Two cavity molds are my biggest problem.
That, and my pot is only a 10 lb bottom pour pot. By the time I get everything in rhythm and working right, I have to stop and fill the pot again.
Now my mold and sprue cutter cool off and everything starts over again.
I need a 20lb or larger bottom pour production pot and a good 6 cavity mold to do what I want to do, but my lead supply dried up so, that's a no go.

I have a 10lb LEE pot too. I invited a friend to help a few weeks ago. One was casting. The other was feeding scraps of lead into the pot. We kept a steady pace while watching the temperature. With the pot on High, we were able to keep the lead level up while casting a steady stream of bullets.

With 1lb ingots, I cast until close to empty and then refill the pot. Casting halts until everything melts and comes up to temperature again.

AJC1 said:

The one thing I know for sure is each mold acts differently. I've only used 3 and two were lee aluminum. This steel mold holds a lot more heat and I have to pump the breaks and slow down a lot. The lee is full speed to keep the heat in.

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Makes sense. My molds are LEE aluminum. They do cool down quickly and can turn out volumes of bullets quickly.

AJC1 said:

There must be an early and late window.

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There is, too early and it will smear.

The tear thing is three fold. One is the lead hasn't "set" completely by cooling down. Another is the mold is too hot. And the last is it may not have filled the mold completely. To solve any of these issues: You should be over-pouring your mold so there is a puddle of lead covering the sprue hole. As the lead begins to cool it will suck a bit more into the mold. Watch that lead on top of the mold. You can actually see it slightly turn color. It's almost like watching Jack Frost in the winter. The lead puddle will turn from bright silver to a dull silver gray color and you will see it freeze up. I use Lee and they can get too hot too. At a good temperature about 5 seconds after the "freeze". Too hot 10 to maybe 15 seconds. If bullets are fracturing, that is usually too much tin or zinc in the mix.

AJC1 said:

Definitely had that on my lee molds. After cleaning up that mess I refuse to cut to early. Solid sprue plus 5 seconds minimum

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I don’t wait quite that long but mold temperature is a factor and brass and aluminum are not the same as steel. I built my machine with two 555 timer IC’s one to adjust pour time the other so I can set a pause time with the mold open for cooling. In environmental conditions I don’t mind sitting by 60 lbs of molten lead, I can let it run without pause up to 230 gn two cavity.

I have a thermometer, but I've been casting for over 30 years and so I let the Force be my guide. "Use the Force, Luke!"
It's not that hard, once you get use to your lead furnace. I have a 10 lb. Lee with a hand ladle. I crank it up full power for 30 minutes to melt the pot and turn it down to 3/4.
I rest the aluminum mode on the top edge to warm it up. It's ready in 8 minutes. I can tell by the flow whether to increase the heat a little depending upon the alloy. Always look at the bottom of the bullet. If they look frosty or get a rough looking surface, you are getting too hot.

AJC1 said:

I'm happy to have you guys around, seems books dont cover it all. Do track mold temp or do you just use lead as an indicator.

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I have a Lyman thermometer in the lead pot and try to keep the molten lead around 750 degrees. Once the mold gets up to temp (bullets fill out and look good), I go at a steady pace, pouring and dumping. I can tell the mold is getting too hot when it takes longer than a 5 seconds for the pools of lead on top of the sprue plate to harden. At this point, I slow down my pace. On my 6-cavity LEE 356-120-TC and 356-125-2R molds, I look for the sprue to harden in 3-4 seconds. Any faster than that, I sometimes don't get consistent fills. Any longer than that, lead may smear when cutting the sprue and the bullets don't drop out as easy.

There's a lot of different things going on when casting. Consistency is the name of the game if you want a pile of quality bullets.

Myself, I don't toss the sprue's or anything else back into the pot when casting. Even temperature, even flow, even mold temperature. I keep a pot on the side and use it to refill my casting pot with a ladle. It's nothing to have a +/- 50# casting session this way with gang molds. The sprue's and other scrap lead go back into the side/feeder pot.

I typically wear a glove when casting and use a gloved hand to cut the sprue's/move the sprue plate. Doing this gives me an accurate read on how hard/soft the sprue's are and my timing for opening the mold. Hence, counting to 4 every time and it gets easier/less pressure to open the mold by hand tells me to slow down. Or speed up when taking more pressure, you'll never know this by "whacking" the sprue plat with a blunt object.

Most casters don't think about the sprue plates themselves. Better/higher quality molds tend to have thicker/heavier sprue plates. They not only hold a more even heat, they have less deflection when cutting making a straighter even cut. Other high quality molds have a thinner sprue plate but have a trough cut into them making 1 large "HEAVY" sprue to cut off. The larger sprue does the same thing a thicker sprue plate does, even heat & less deflection.

On molds with light/skinny sprue plates will have less tear out if you make a larger puddle on your sprue plate. I've had to make huge sprue puddles connecting the 2 holes on lee 2-cavity molds before to get them to quit tearing holes in the bullet bases. The trade off was the small sprue plates got too hot real fast.

For those that like to play whack-a-mole with their molds the easiest way to keep the sprues from tearing the bullet bases on their lee molds is to keep a damp cloth handy. Simply pour you bullets and touch the damp cloth to the sprues cooling them off (+/- 2 seconds) then whack away. No more tearing!!!

Your alloy will make a difference too. Many times I am in a hurry so I cut sprues a bit soon. I just live with a bit of a crater torn out of the bottom of the bullet. I can’t shoot a pistol well enough to notice the difference. I have a dozen Lee molds, 2 and 6 cavity in obviously several calibers, styles and weights. After years of playing with alloy mix I’ve settled on wheel weight and soft lead 50/50. Most of what I cast are not high velocity bullets, 380, 38 Special, 40 S&W, 45 Colt , and 45 acp. Harder alloy gave me more grief, and I didn’t need harder bullets.

Apologies if it's already been mentioned and I missed it, but with my iron molds I'll touch the sprue and plate to a wet cotton rag to help cool it quickly, maybe for 1 or 2 seconds depending on how hot things are. This helped speed up my production hugely when using my iron molds.