What is usually the cause of a dimple where the sprue plate cuts?

[Manns50]

Trying to remember some things, get my rhythm back. Cast up a pot full tonight. Haven't looked through for rejects yet but I did notice there was a small period there where this was happening. I adjusted a couple things, as in waited a little longer before opening the sprue plate, Waited a bit longer to let the mold cool a tad and adjusted temp of pot a bit and it seemed to clear up. Was using a Lee 6 cav SWC mold. was running about 700-720 usually but adjusted both ways a few times.

[MarkP]

Sounds like Shrinkage.

[Taterhead]

If it is a dimple torn out from where the sprue was attached, that is from cutting the sprue too soon before the sprue puddle is fully setup.

[Bazoo]

I’d it’s a tit on the bottom of the bullet, it’s from cutting the sprue too cool. The cutter will jump the nub.

[Manns50]

If it is a dimple torn out from where the sprue was attached, that is from cutting the sprue too soon before the sprue puddle is fully setup.

This was the issue I believe because you described it exactly as it was happening. The six cavity mold takes a little longer to cool down if I remember right. I started off with the two cavity years ago but I do remember I had to make that adjustment. I was waiting till it flashes off but that is not seeing the center portion of the cavity is cooled

[Sasquatch-1]

On the pistol bullets I cast I don't worry about it too much. I have found that if I let cool down a few extra seconds after the sprue hardens, it doesn't seem to occur as much. The biggest problem I have with it is, when running through the Lubrisizer is I get lube on the bottom of the bullet.

[Manns50]

Ok I sorted through them and for my first casting in years, this dimple was the main reason I rejected about half of them. I had used a 2 cavity mold for a long time before going to the 6 cavity years ago. When I made the switch I remember I had the learning curve of realizing the 6 cavity takes a bit longer to cool and holds more heat naturally. Guess I had to learn this again. The other main reason for being a reject was the base of the bullet not filling out at the base (having a slight rounded edge at the base). I played with the pour rate, I was taught not to have it fill the mold very quick and not very slow. About 2 seconds maybe little less.
What is some opinions on the fill rate of a mold?
Have seen some like the pot set extremely fast, maybe I need to speed it up.

[pworley1]

The dimple is most likely from cutting the sprue too soon, as others have said. The rounded bottoms are usually caused by too little sprue and or pouring to slowly.

[justindad]

On my bottom pour RCBS pot, I get fill out issues if I fill a cavity in much less than 2 seconds. I also pressure pour by inserting the nozzle into the cone of the sprue plate. This was not an issue when I used a Lee pot. I think the biggest cause is that the RCBS stream has a large diameter than the Lee pot did, so gas cannot escape out the sprue plate as easily.

[onelight]

It may also be caused by not leaving a large enough puddle on the sprue plate to fill the base as it solidifies/shrinks in the mold.

[The Dar]

Trying to remember some things, get my rhythm back. Cast up a pot full tonight. Haven't looked through for rejects yet but I did notice there was a small period there where this was happening. I adjusted a couple things, as in waited a little longer before opening the sprue plate, Waited a bit longer to let the mold cool a tad and adjusted temp of pot a bit and it seemed to clear up. Was using a Lee 6 cav SWC mold. was running about 700-720 usually but adjusted both ways a few times.

If you're talking about a divot in the base of the bullet where the sprue plate cuts the sprue it could be that your sprue plate is too hot before cutting. I've had the same problem. I tried a small clamp on desk fan. I run my lead from 720 -730 degrees and put the mold under the fan for about 8-10 seconds after filling the mold (Lee 6 cavity). Solved the divot and makes nice sharp bases.

https://www.walmart.com/ip/Comfort-Zone-6-2-Speed-Portable-Indoor-Desk-Fan-W-Clip-Adjustable-Tilt-Rotates-360-White/21903490?athbdg=L1200

[stubshaft]

Cutting the sprue too soon.

[Dragonheart]

Simple fix, run two molds simultaneously, alternating. This allows more cooling time and speeds up production.

[Manns50]

I just cast some 10mm 200g yesterday evening with an RCBS and didnt have any issues, I think I was consciously waiting a little longer as well it being steel retaining heat better. Will hit the Lee soon enough and will give it a bit of pause or lower my pot temp.
Love that RCBS mold, bullets were just stunning!