Voids in the hollow base. Any idea why?

[vogironface]

I have voids in the hollow base of my 50 cal mini balls.
The mold is a lee 500-354-M and cast out of pure lead.
I have altered temperature and the angle I hold the mold as well as the speed I pour. I can't figure out what is causing the void. It does not happen every time but most of the time. Any thoughts?

Thank you.

64327

[303Guy]

That looks like a shrinkage void caused by the nose freezing before the middle and drawing metal up from the still soft base as the centre freezes and shrinks. Maybe the top of the mold needs to be warmer?

[runfiverun]

pin temperature.
that is classic.

[stubshaft]

+1 on pin and mold too cold.

[btroj]

For pure lead I always turn the pot up to max temp. Get the mold good and hot and keep a good casting rhythm going.
That pin needs to be hot and stay hot to avoid that void.

[44man]

I have had that problem forever with certain molds, others not a problem. I tried everything from cutting vent lines on the pin to heating the plug with a torch, made it smoking hot and charred the handle. I cast fast and very hot with lead and pot as high as they would go.
I still had one mold that kept doing that for the Minie' and another for a 12 ga slug. Still drives me nuts! It did not happen with every one but each side of a good one that hole was there.
I also tried pouring every way I could get lead in the molds.
I cast a pile of .54 Minie' balls with a friends mold and never had a bad one. Why did his work with just normal casting----I am at a loss.
The gremlin strikes! [smilie=1:

[vogironface]

I think you guys have nailed it with temperature. I have only used this mold a few times, all in the dead of summer and casting hot and fast with few problems. This time I noticed the void and started experimenting which meant I was casting, thinking, tinkering casting etc. I am sure the pin never got hot enough or the mold was never hot enough. I will try again getting the mold and lead plenty hot.

Thanks!

[Harry O]

I have probably cast 10,000 hollow-base bullets by now (41LC in CAS shooting). That is a classic "not-hot-enough" shrinkage void. It is important to get as large a "glob" of melt on top of the mould as possible (before it drains off the sides). The glob has to be hot enough so that when it finally flashes over, there is a dimple over the top of the sprue plate hole. It is usually 12 to 15 seconds before it flashes over for me. That shows that the melt on the sprue stayed liquid long enough so that the glob was able to feed the inside of the mould before the sprue hardened.

Without a dimple, you have a void somewhere, even if you cannot see it. This can be verified by weighing. A bullet from a sprue without a dimple will have more weight variation than a bullet with a dimple.

Heating the "pin" or "plug" helps somewhat, but not as much as having a dimple in the sprue. I rigged up a wire coil over a candle to hold the plug while I am opening up the mould, shaking out the bullet and giving it a cursory look-see. That also helps by keeping the pin smoked.

[ken s]

I cast .58 minis' and have it happen some times, but...when I 'giggle' the mould when I pour It seems to settle the lead down and that won't happen...try it..just a little jog as soon as you pour while the lead is still liquid in the mould...Ken

[geargnasher]

Pin too cold, cast faster and don't let that pin stay out of the blocks for a split-second longer than necessary.

The temperature of the lead, if it's pretty close to pure, can be turned way up in this instance. If there's no significant tin in there, or you aren't concerned with keeping any trace that IS there, go ahead and turn the pot up to around 800 degrees, the lead will impart more heat to the blocks each pour and the block and pin heat is what gives the fillout. Lead isn't a whole lot more fluid at 800 than at 650, but that extra heat in the lead gets pumped into the mould where it's needed to keep things flowing and filling inside.

Ken's "Jog" technique also might help, and pouring at a moderate rate so the air being pushed up from the skirt along the pin doesn't get trapped at the pin's point. Tilting the mould slightly should help too, although I saw that was already tried in the OP.

Gear

[44man]

I did all of that Gear but some molds drive me nuts. Only a few. I get a good pour going and inspecting later shows half with the dreaded gremlin hole.

[runfiverun]

you might just have to polish the jebus out of it or round the nose over on it.
a real pointy tip will exchange heat real quickly.

[vogironface]

thanks again for everyone including the anti-social Texan. I guess the question would be does it really matter?has anyone ever compared accuracy with these with the voids vs those that don't? My knee jerk reaction is to not use them but perhaps it would be just fine.

[Cap'n Morgan]

I think Harry nails it pretty good. I wouldn't be surprised if voids are the rule, not the exception. Most times we just don't see it, but in this case with the hollow base, we have a "window" to the core of the bullet where the voids are most likely to appear.

[HARRYMPOPE]

I got around it in my .577 Minies by letting a 3/4 full ladle of metal pour in before topping off.Its messy but produces bullets with no base pin holes.But they really shot only a bit better than the ones with the holes that had the weight vary by quite a few grains.A musket with crude open sights shooting about 2 MOA (on a good day)isn't a bullet testing machine.

[snuffy]

The mold is a lee 500-354-M

http://leeprecision.com/mold-500-354-m.html

Since this is a lee HB mold, the base pin stays with the mold. It's difficult to keep it hot, also, it's made of aluminum, so it cools faster.

I have one that makes a .458-405 HB 45/70 boolit. I've had fits with it NOT forming nice clean HB cavities. I place the mold on my hot-plate between casts to heat the steel bracket that holds the base pin. Then I use a lyman bottom pour ladle to pressure cast by cramming the ladle against the sprue plate while the mold is held flat. If not held against the hot plate for about 30 seconds to a minute, and NOT using the pressure cast method, I get voids like in the OP's picture. This is when using the small lee 8 pound melter with 40-1 mix.

[beagle]

I'll go along with the lack of heat problem in this particular case....but, our cast bullets are full of voids. No way that I know to eliminate them.

I thought this was just a base thing until we impact coated some cast with moly using jewelers polishing media. Then, they appeared all over the place. We even selected perfect looking specimens and they still showed voids. On the ogive, nose, bands....all over.

Just like making sausage. Do your best and don't worry about what's on the inside./beagle

[HARRYMPOPE]

When moly coating was in vogue in the CBA in the 1990's Lloyd DeVore told me the best thing it did was expose the voids on the bullets and that the Moly itself was worthless.he omited the moly and tumbled his bullet in steel shot only.I noticed that on some mold deigns it would expose voids on the nose and bands occasionally as well.Some deigns i never found them on for some reason.I i intentionally shot some of the culls(RCBS 180 Sp) and surprisingly in my 30 BR very few went out of the groups much more than 3/4 MOA.More stayed in than went out truth be told.The worst had a base inclusion about 1/8" wide by about 1/4 deep and only went 1.5" high and right @ 100.Shooting culls is worth the time i think.