Voids in bullets

D

Dre_sa

New member
Hey guys,

I'm starting to cast some bullets for my martini henry, a bloody expensive project to get this thing shooting for sure, but I'm learning lots and having some fun.

I do have a question for those with more experience than I do (and yes I have tried the search function)

I set up my bottom pour pot, put some 20:1 lead in it, got everything heated up and started pouring some bullets.

I noticed while taking a wee break that some of the bullets had a void in them, or had what looked like a dent in the side. closer examination showed that these holes were happening along the seam where the two halves of the mould meet.

I did manage to get a few (about a third of them) good looking bullets of consistent weight.

My question is what am i doing wrong?

is it the temperature of the alloy? the mould?
is it the rate of flow?
something wrong with the mould itself?

Thanks for the help and any insight you more learned folks may be able to offer.
 

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I had a similar problem before and it appeared to be due to a lack of venting on the mold. I cleaned the mold real good and used a razor to clean out the vent lines. When cleaning out the vent line be very gentle. After these steps the problem disappeared.
 
1. Get a hot plate and while the lead is heating, heat the mold on a small flat griddle/under a small 1 cup pot (i.e. a dutch oven)

2. Cast a 720-750 degr for 20:1

And here's the heavy bullet/void solution:
3. Don't contact pour. Instead let the lead flow freely into the mold with ~a 1/4" gap from the pot's spigot to allow air to escape.
 
Big bullets, you gotta pour em fast. Use the heat mentioned above, and make sure that your spout is open and clean and it is pouring as fast and as large a stream as you can get out of it. Make sure pot is nearly full too (= more pressure). Quite often folks have to use a ladle to get enough lead into the hole fast enough on a big bullet. Some pots just won't fill it completely. Make sure the lead stream is centering on the hole too, don't let it hit the indention on the sprue plate and kind of swirl down into the hole. Flood it as fast as you can.
:) Good luck!
 
others have covered just about everything I was going to suggest...

Remember, the mold is a large cavity you are filling with metal. It is already full of air, so in order to fill it with metal, the air has to go somewhere. If it cannot escape out the sides or top, it will be trapped inside the mold, creating a void. A bubble of air inside the solidified metal.

Do as suggested.... clean all vent lines first.
Adjust your pour as suggested.... fastest flow possible, to get the metal into the mold before it starts to solidify.

Pre-heating the mold to 400-500 degrees will help keep the metal from freezing off too soon.

Your driving bands look good, with sharp edges..... I'd bet on a venting problem.
 
Interesting.
I've seen voids before on some (long) 437 gr .44 caliber bullets that I cast, but nothing like that.

I honestly don't know what could cause that, that hasn't already been mentioned. All I can offer is what I used to do for big bullets:


I haven't run anything close to pure lead (or even your 20:1), so I haven't needed to run the melt as hot as you may need.

But I did cast many hundreds of 390-450 gr .44 caliber bullets a few years back in 1-cav and 2-cav brass and aluminum molds.
To get keepers:
I had to run the melt pretty warm (~750+ F with WW+2% alloy; absolute minimum of 725 F; replacing tin as I skimmed oxide).
I had to keep the mold blocks very hot, to the point that the bullets were almost always frosty.
And I had to use a large ladle to pour all cavities as quickly as possible. ('Air gap' method - no sprue plate contact.) Though some bullets could be done with the RCBS 'fin' ladle, I often had to use my Lyman ladle. (Which I don't like - it never stops oxidizing when heated and constantly adds slag to the melt.)


I have a 450 gr muzzle loader bullet mold sitting here, waiting for its chance at the casting bench, and I intend to use pure lead with just enough tin for decent fill-out. To be honest... I'm not looking forward to using it.
 
So I think i've figured it out guys.

Per your suggestions, I cleaned off the vent lines in the mould, made sure it was about 1/4" from the spout, got the alloy good and hot and upped the flow rate.

I did see an improvement, but the holes just got a little smaller.

I then decided to see which of the two cavities was acting up so I did batches of 10 from each, using only one cavity in a string.

the bullets came out perfect.

I tried filling both cavities again, and the voids showed up again.

so i did the rest of the casting session alternating between the two cavities, not both at once.

The results were much better. more consistent weights, better fill out and fewer rejects.

Thanks all for the help and suggestions!
 
Interesting.

If it were me, I would see if getting some more heat in the mold would help with that. It sounds like the alloy is cooling too quickly once poured into the cavities.
 
Ou on a limb

I'll go out on a limb, and hand everybody a saw.

Those boolits DON'T look like they were cast with 20-1 lead!

I set up my bottom pour pot, put some 20:1 lead in it, got everything heated up and started pouring some bullets.
Click to expand...

Very obvious signs of antimony on the surface of the boolits. Also signs of dirt inclusions on the surface of the boolits. Flux the lead until that crap goes away. BUT that shouldn't matter, you've got serious problems with the mold vent lines and your technique.

20-1 lead should cast just fine at 650 degrees, it needs a lot less heat. As long as the mold is up to temperature. I have NEVER seen frosted boolits with a 20-1 lead tin alloy. Frosting is caused by antimony. Those boolits are heavily frosted.

What caliber is it? What does the boolit weigh? Who made the mold?
 
This is what my 20-1 boolits look like. Shiny and well filled out.

P4260022.JPG


Those are .460-420 for my 45-70. That's also pure lead from Midway, and pure bar tin from Roto metals. Those were cast from my 4-20 Lee pot @ 675 degrees on my P.I.D. controller.

The mold was a group buy over at cast boolit forum, a lee special order 6 cavity.
 
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