Mold leaving little tabs/burs on cast bullets

[300leonidas]

Good Afternoon Friends!

I've got a couple of molds that leave little tiny tabs or burs @ the seams on the boolits when they drop out of the mold. I'm using Lee Molds and they didn't always do this. I imagine the mold has gotten gummed up a little and perhaps at the studs that keep them from closing completely tight. Any thoughts on a solution to this problem? How does one get a mold to stay completely closed so none of these little burs develop?

Thanks!

[Winger Ed.]

If it's good & clean and closing properly, you might be running the pot a tiny bit too hot.
The more & more Tin in your alloy will often try to do this too at your 'normal' pot temp.

[Delkal]

Give your mold a close inspection and look for small specs of lead stuck between the halves. They are usually tiny and melted flat but if you see them gently try and pick them out.

I know with proper technique this should never happen but sometimes they magically appear.

[JonB_in_Glencoe]

If you are using Lee 6 cavity molds, you have to be careful to NOT squeeze the sprue plate handle during pouring. When you squeeze that one, it actually opens the mold halves a little and causes the fins and flashing you describe.

[Dusty Bannister]

Lee has two different types of two cavity molds and have different alignment systems for the mold halves. Also the alignment areas require a little lube from time to time. Clean the molds if they are "gummed up a little" but I am not sure how that could happen if you are treating them right.

Old style or new, 6 cav or 2 ?

[Baltimoreed]

Smoke your molds good too to keep anything from sticking to them after a good cleaning. Most of my molds are 2 cavity so I squeeze them tight.

[THE_ANTIDOTE]

What Delkal said. At some point when I started with casting I too started seeing flashing. I thought I was doing everything right, my temps were right on, my rhythm was good, my molds were all prepped...I couldn't figure it out. One day I was casting and as I closed my mold after dropping bullets I noticed a bit of light coming from the inside of my mold. Turns out, I had gotten too relaxed on my handles and not applying enough squeeze to the handles...could have been over confidence...could have been I lost some motivation, I was also using thicker welding gloves. I changed over to my mig gloves which gave me a better feel so I was able to better apply the correct amount of force to keep my mold fully closed during pouring through out my session. I did have a pair of handles that I would require frequent tightening or loosening of the bolts that hold the molds in order to assure positive alignment of the mold halves. In my case, it was user error and like Dallal mentioned...technique.

[Apple Man]

Give your mold a close inspection and look for small specs of lead stuck between the halves. They are usually tiny and melted flat but if you see them gently try and pick them out.

I know with proper technique this should never happen but sometimes they magically appear.

If you are using Lee 6 cavity molds, you have to be careful to NOT squeeze the sprue plate handle during pouring. When you squeeze that one, it actually opens the mold halves a little and causes the fins and flashing you describe.

You guys nailed it.

I keep a small piece of steel wool next to the pot, wipe off the sprue plate whenever you see buildup.

[300leonidas]

My molds are all the Lee 2 cavity Molds. I will inspect more closely and see if I can see what might be causing them to not close all the way.
thanks!

[Ia.redneck]

Sometimes lead will get in the vent lines if the lead is going in too fast. Slow your pour a little. A half turn on the adjustment screw will make a big difference.

[405grain]

Before you begin a casting session, with the molds in their handles, open the sprue plate and hold the closed mold blocks up to the light. If you see any light coming through between the mold blocks the mold isn't closing properly. I've found that this is usually caused by two things: The most common cause is that a tiny spot of alloy has found it's way in between the mold blocks, and has created a shiny spot on the face of one of the molds, or is in one of the air vent grooves. There are several ways to remove this, but be cautious not to damage the mold. First, with the molds at room temperature, I'd try scraping the lead away with a small flat stick or toothpick. You could probably use a piece of plastic as a scraper too. You could also try using a used and worn out toothbrush, (but make sure to throw it away afterwards). On iron molds I use an ink eraser to scrub away any lead on the mold faces or the bottom of the sprue plate, but I'd be hesitant to use this on an aluminum mold.

The second area that might be preventing a set of molds from closing completely is the holes for the guides on the mold blocks. Usually, though not always, there are rounded pins on one mold block that fit into matching holes on the adjacent mold block. These keep the mold halves in alignment when the mold is closed. There has to be a very small amount of play between the mold blocks and the handles in order for the blocks to wiggle around and align as the mold is closed. This minute amount of play can cause the alignment pins to strike the edges of the alignment holes as the mold blocks are closed. Over time this contact between the alignment pins and the holes can cause incredibly tiny dents to form around the edges of the mouth of the alignment holes. Sometimes these dents will become just enough to prevent the mold from fully closing. (were talking about only a few thousandths of an inch of gap left open - just enough for light to pass between the mold halves and maybe for some alloy to "fin" into an air vent or make the bullet one or two thousandths out of round.)

The way to correct this is to take a counter sink and , by hand (no power tools), gently rotate this on the alignment hole only one or two turns, just enough to remove any of those tiny dents along the edge. Don't use excessive pressure - you're not trying to create a chamfer along the hole's edge. You want to do this just enough to clean up any imperfections around the mouth of the hole so that the alignment pin will fully enter it. Quite often, after this "deburring" the mold blocks will close with a light tight alignment.

[jsizemore]

Sometimes the alloy and/or mold block temps are too high.