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destrux
05-07-2015, 11:00 AM
The last two casting sessions I've done I've been having a terrible time with air pockets or voids inside the base of the bullet. Now, I don't know if they're gas bubbles or just voids, but when I drop the bullet the side of the base shrinks and sort of caves in on itself. Sometimes you can actually watch it happen. It looks like someone whacked the side of the bullet with a tiny hammer and dented it. I culled all the dented ones, which was about half of them, and shot the normal looking ones (that appeared to be completely filled out) only to find that I'm getting fliers that are all over the place (some were 12 inches away from the main group at 100yd). I collected some of the shot bullets and found the sides of the bases caved in, so there were voids in a lot of those too even though they looked fine. Last time I cast a large batch with this mold I had fill out problems with the base, but culling the bad looking ones left me with good shooting bullets.

Any ideas on what can cause these voids? Something in the melt?

I tried different casting methods, I tried pressure casting and pouring a generous sprue and neither method solved it. I'm casting at 650 degrees and using straight clip on WW lead that I smelted myself in a separate pot. The mold is a Lee 230gr "blackout" mold which I've previously gone over to make sure the vent lines are open, I'm lubing the sprue plate with a q-tip using a very light coat of two stroke synthetic oil.

I'm considering just giving up on this mold and buying an aluminum NOE 247gr mold but I don't know if it will give me the same issues.

mongoose33
05-07-2015, 11:23 AM
My first guess would be your mold is not hot enough. I'd also think you may want to go hotter with your melt. You might also consider adding just a bit of tin to help w/ fill-out.

One thing I noted in my casting is that the order in which I fill the cavities matters. In a six-gang mold, the cavities nearest the handles cool faster (due to the handles drawing off heat) than the ones furthest. Solution was to fill starting at the ones on the handle-end and moving outward. This keeps those close cavities in the heat longer than if I go the other direction, and it solved my fill-out problems.

Litl Red 3991
05-07-2015, 11:55 AM
........., I'm lubing the sprue plate with a q-tip using a very light coat of two stroke synthetic oil.
.......

What could be the source of the gas you feel is causing those voids?

Toymaker
05-07-2015, 01:14 PM
I can't speak regarding bullets, but with roundball it is an epic problem. Some years ago there was an article in the NMLRA MuzzleBlasts magazine about this. I was unsure, so I used a sharp knife and rolled a roundball under it until it was cut in half. Sure enough, there was a void. It is a true void, not a gas bubble. According to the article it is caused when the hot lead cools and contracts. The article recommended a casting temperature between 700 and 750°F; good pre-heating of the mold; holding the mold TIGHT against the ladle spout or bottom pour spout longer than needed to fill the mold (practice and experiment) [pressure casting?]; and getting a good button. Speed in casting was also mentioned so the mold wouldn't cool off. For me it happened with 54 caliber ball more than 40 or 45 caliber. I weigh all my roundball, 5 grain variance. Using their recommendations I cut my rejection rate from 30% to about 10%. I use a single cavity mold. I wear welders gloves because, using a bottom pour pot, you can get a geyser of molten lead if the mold isn't tight against the spout or there's a bit of lead keeping it from being TIGHT.
When casting bullets (.451/535 grain, .459/405 & 500 grain) I do much the same but ladle cast only and increased my temperature to 800°F and get more consistent results and weights. Hope this helps.

gwpercle
05-07-2015, 01:39 PM
More heat. start out around 750, when boolits start getting frosty back down to 725.
That "light coat" with a Q-Tip is contaminating your bases. Give it a coat about one molecule thick .
I never could get the two-stroke coat thin enough not to contaminate so I started using Liquid Wrench Dry lube on a Q-Tip . You can coat the underside of the plate, the top of the block and not get any contamination.
I started using Permatex Anti-Seize Lubricant to lube the rest of the mould because being thicker it doesn't migrate and contaminate the boolits as easily as two stroke oils . It takes so little to lube it's real hard not to over do it. Don't give up , casting has a learning curve that just takes practice.
Gary

stubert
05-07-2015, 01:42 PM
try lubing with dielectric silicone grease.

CJR
05-07-2015, 01:44 PM
Destrux,

On most of the sprue plates on my gang moulds, I have cut a groove connecting the pour holes. Years ago, the NRA recommended this. Likewise, I flux my newly melted lead alloys a lot if I haven't previously smelted/flux cleaned it. This removes most of the metallic inclusions in the alloy. Then when CB casting, I run my lead temperature a little hot so that the alloy stays molten a little longer in the sprue groove. This allows the alloy to gas off some, the CBs to fill-out better,and the final CB weight spread is smaller. Essentially, my casting pace slows down a little, but the quality of my CBs improves. LBT advertises their sprue plates as minimizing gas pockets.

Hope this helps.

Best regards,

CJR

destrux
05-07-2015, 01:49 PM
If I go hotter (around 700) they seem to get worse, with nearly every bullet having a void. At 650 I have a molten puddle on the top of the sprue plate for about 3-4 seconds. Then I wait another second or two to cut the sprue, and drop them on a cloth.

CJR what sort of flux are you using? I use a pine 1/2" dowel to stir my lead pot instead of fluxing. It was a tip I heard on here. Maybe that's not enough to flux it? I generally get about a half teaspoon of grey crud off the top each time I sit down for a ~150 bullet casting session. I stir the pot with the dowel and scrape around the sides to get the impurities that stick to the inside of the pot.

I saw NOE recommends graphite powder to lube their aluminum molds so I guess I'll try that instead of the two stroke oil to see if it helps.

Right now I need to wait on another Lee mold because I just tried to make this one plain base on the lathe and screwed it up.

Echo
05-07-2015, 01:51 PM
My dos centavos - more heat, and a sumptuous sprue puddle. I'm guessing the alloy is shrinking during solidification, and doesn't have enough excess (in the form of a sumptuous sprue) to draw from. Adding a little (2%) Sn is a good idea, too...

Wayne Smith
05-07-2015, 02:01 PM
My dos centavos - more heat, and a sumptuous sprue puddle. I'm guessing the alloy is shrinking during solidification, and doesn't have enough excess (in the form of a sumptuous sprue) to draw from. Adding a little (2%) Sn is a good idea, too...

What he said. All alloy shrinks and draws from the sprue to fill in the shrinking. If the mold/alloy is too cool the sprue hardens too fast for this to happen, if the sprue is too small there is not enough alloy.

44man
05-07-2015, 02:30 PM
Exactly why I ladle pour but 6 cavity would be a problem. I hold the ladle tight until the shrinking boolit pulls all it needs from the molten lead in the ladle. The sprue will freeze first and deplete the mold. 3 to 4 seconds is too soon. More heat.
Pure lead rb's need 800.

bangerjim
05-07-2015, 02:49 PM
More heat in your pot.....HOT mold (heated to full casting temp on a hotplate).......more Sn. I always use 2% Sn and never have any voids.

The only time I ever saw that was with a cold mold and under-temp lead in the pot.

To REDUCE Sn back into your casting pot, use beeswax to minimize the garbage from burned sawdust and to get mirror shiny surface almost like magic.

Hope you find your solution.

fredj338
05-07-2015, 03:11 PM
Could be couple of things. If you are using a lube for the spru plate, if it's too thick, you'll get voides on the base. Make sure the spru is large enough to allow some shrinking. The other thing could be venting. I had one iron mold that always gave voids. I lightly beveled the top of the molds where they come together. It creates a tiny vent under the spru plate. Now the mold produces perfect bases. Something to try. You can always try pressure casting, holding the spout tight to the spru plate for the fill, then over flow for the spru. This also works for me on certain molds where I struggle with fill out, like some of my HP molds.

bangerjim
05-07-2015, 03:57 PM
Glad you brought that up! Pressure casting will/should eliminate any voids at all!

I also have a couple molds that give good drops only when p-cast.

With a good level of Pb in your pot you will have a decent head pressure forcing any air/gas out of your cavities.

banger

mongoose33
05-07-2015, 04:00 PM
If you do the pour correctly, you can see a small dimple form in the sprue puddle as the shrinking boolit in the mold draws more alloy in. This only happens if it's hot enough--if the sprue hardens too fast (as others have noted), there's nothing to draw from).

To me, one of the signs it's time to cut the sprue is that dimple having formed.

CJR
05-07-2015, 04:53 PM
destrux,

I've been using Marvelux for awhile and get it from Brownells. Also, if you ladle cast get in the habit of always stirring the pot before filling the mould.

Best regards,

CJR

Toymaker
05-07-2015, 05:03 PM
HOT mold, fast casting. It would be ideal if the bullet solidified from the center core to the outside, but it ain't gonna happen. The outer edges are going to solidify first. You want extra molten lead available for the shrinking center core to draw from. You want the core to solidify before the button. A large button, staying liquid so the core can draw lead while it shrinks, takes practice and experimentation. Keeping the lead HOT so the ladle, pressed against the sprue plate, has free flowing molten lead available to the core is easier. Using a bottom pour is the same - HOT lead so the pour hole doesn't freeze up, mold pressed tight, wait, wait and wait for it, them back off and make a button.
It takes time to develop the knack, experiment, practice, there's some great people and information here, but we can only provide guidance. You have to do it. You're on the learning curve. Here's a promise - in six months you'll be telling someone else how to overcome this.

williamwaco
05-07-2015, 05:18 PM
Classic symptom of inadequate sprue. Your sprue puddle should be as large as a quarter and half again as thick. (For each cavity) It should take three seconds minimum to solidify. This means that after filling the last cavity you should count two seconds then tilt the mold to the side and the sprue should pour off like water. If you can't, your mold is not hot enough.

when you reach this temperature, resume your normal cadence.

44man
05-07-2015, 05:26 PM
I have never called it pressure casting, only lead feed. Pressure in itself does not work except to push out air. I cast two boolits with one ladle full. If half a ladle made a bad boolit I would eat it. It is bunk to keep a pot at a certain level.
You see what others say, FEED YOUR LAWN!

popper
05-07-2015, 05:27 PM
That is a long skinny boolit so you need to be >700F. Maybe higher if a 6C mould. Your sprue is hardening too fast and probably (if pour rate is fast or pressure casting) a big cool sprue will stop venting at the base/plate. Drag a knife edge across the inside top of the blocks - careful around the cavities - just 'break' the edge. I use synthetic 2 cycle oil, apply with q-tip when the mould is hot then wipe with a paper towel till you can't see it anymore. Some tin may help. IIRC that is the BT mould, any voids in the base will really cause flyers even though the pressure is low.

runfiverun
05-08-2015, 11:04 AM
I have that mold and pour both cavity's full at the same time, I line up both sprue holes with my outlets and give them a good stream of alloy.
the longer boolits like to be filled hard and fast.
my initial thoughts was the sprue plate lube getting into the mold and gassing off but that usually affects the surface of the boolit in the form of wrinkles and such.
an internal void is a different matter all together.
I have seen lino-type pigs poured into open molds form a void, just from the way the alloy was poured into the triangular shaped mold.
but a small sprue one not sufficient in size to feed a cooling boolit will give you voids and small base drive bands.
you may just not be running the mold hot enough and the alloy is trying to cool [heat being drawn off into the mold] while you are still filling the mold.

bangerjim
05-08-2015, 02:01 PM
I bought one of those ole antique long bread stick CI molds to pour certain alloys in.

Found out REEEEEL quick they formed voids and cavities internally like crazy.....for no reason. I could NOT figure it out! Poured into the hot mold form from my re-melt pot at at least 730F or so. My 1# RCBS/Lee/Lyman ingot molds do not do that. Voids in ingots do not matter, but I could not get a single one to pour without holes. Got PO'd with the dang thing, so I never used it anymore.

Hot Pb and alloys will do strange things at times!

country gent
05-08-2015, 02:52 PM
Look the mould over under magnification for burrs and square corners at top mating surfaces as these can cause air locks that promote voids. With fine sand paper backed on a flat surface just break the sharp edges on top of blocks. You just want to see the fat under magnification. With the point of an exacto knife insure all vent lines are clean and clear. Make sure moulds are opening and closing freely also. Keep flow rate as high as possible long bullets need a fast fill rate, In diecast industry casting machines have a "Shot tube" that litterly forces metal into die or mould under pressure preventing voids. SOme moulds can be very fussy the first few times casting till they break in, ussually 2-3 sessions. Clean mould with dish soap water and tooth brush completely. Run your alloy around 725*-750* and pre heat the mould while waiting for alloy to melt. Fill and cucle as fast as possible. pour a large sprue possibly allowing a little to spill over the side of the mould. Heres where alot make mistakes, Not only wait for sprue to harden but watch it closely to see it "Frost Over" ( looks like frost flowing accross the sprue similar to your yard on a late fall morning) when this occurs give a 3-5 count and base should be filled and cooled to point of being ready to drop safley. If you really want to make bullets quick buy a second one of this mould, fill one as above set aside and fill second break sprue on first while other is cooling running this pace will negate the cooling time of one mould as your filling while its cooling. Keep a quick consistent pace dont "admire" bullets and do everything the same

destrux
08-06-2015, 03:13 PM
I finally figured this out once and for all. I tried adding tin, more heat, different lube, no lube, vent lines, etc... but all were only incremental improvements without being a complete solution.

But...

The pour spout on my Lee pot was pouring so fast it was frothing the lead, compounded by the the long freefall into the deep 230gr mold, leaving it full of air pockets and and causing the appearance of wrinkles by splashing lead up into the base area while the stream was filling in the tip. The small lead splashes were hardening and only partially remelting into the bullet when the fill level in the cavity reached them. Pressure casting didn't even fix it.

I figured this out last night when I let my lead pot run nearly to the bottom while trying to cast ONE good 230gr blackout bullet (they were still awful even after adding 3.5oz of tin 95SN5CU solder as suggested). When the head pressure in the pot dropped to the point the lead was barely trickling out of the nozzle I started getting perfect bullets. See I never let my lead pot run low like that, I always run it topped off, never below 3/4 full. I was too frustrated to bother filling it this time though. So I took some pliers and bent the valve handle on the pot so it can't open as far. Then I topped up the pot, checked the flow rate to be sure it was still very slow, and cast a couple hundred perfect bullets with very few rejects. It was also much easier to cast without spilling lead all over the place like I usually do.

I also found it's important to hold the mold close to the nozzle to reduce the distance the lead falls, or the problem returns. About 1/4" from the nozzle seems to work.

This problem probably doesn't come up much because the high nozzle flow didn't seem to cause problems in my shorter and fatter bullet molds, only these super long skinny ones.

popper
08-06-2015, 03:33 PM
Had the same problem with pouring 170gr, not as bad as yours. I put some flat washers on the bottom arm to limit flow. I think the to screw is to adjust flow but I removed mine and put a tap wrench on the stem for weight.

Blackwater
08-06-2015, 07:03 PM
Voids really got to me when I started casting the big, long, heavy bullets for BPCR. I started out with 50/50 WW/soft lead. Voids in EVERY bullet. Some sages told me I couldn't use an alloy with any antimony in it, like WW. This didn't make sense to me, so I tried the same alloy again, and ... predictably .... got the very same results. Frustrated, I mixed up some simple binary lead/tin mix, and ... believe it or not ... BINGO! No more voids. I got other advice like reaming the sprue hole out a bit larger, but since I was getting great bullets with the simple lead/tin alloy. I never tried that. Could be an option if nothing else works, though. Have always cast my RB's and ML conicals from soft alloy also, and no WW's, and have never had a problem, but this pursuit of ours holds all sorts of surprises to perplex us with from time to time. I'm still not sure what the antimony does, unless it makes the pour solidify too fast, and thus creates the voids from the internal pressures? I know just enough to know how much there can be that I don't know about, that when I find a fix, I just let it go at that, and just keep reading and searching until I find a good explanation I can accept.

Welcome to casting, and its mysteries!