‘New Casters’ . . . forensics of a casting session
What does our work say we are doing?
I cast for a long time before I really understood what I was doing…heck, you just melt some lead and pour it in a mould…right? If the bullet gods are smiling on you everything goes well. If not…hmmm…maybe I wasn’t holding my mouth right? How do you figure out what happened? What can I do next time?
My answer now, after making all the mistakes, is that casting is very basic…you need to have a few things aligned properly to get that hot lead to come out of the mould the way you want it…nice shiny round bullets. In this article I don’t want to start with the lead and describe its blending for specific purposes, I want to assume that we are all using clean ingots of range scrap, wheel weights or store bought lead, or some mix you put together that works in your pistol or revolver. That would be too technical for the discussion today…I want to get you to learn to read your work as you do your work so that you can make little corrections during the casting session and fine tune for success in every batch you run. Recognize the subtle signs that reflect what you just did…know what they’re saying and make a correction right then.
In the picture below there is a story within the casts and the sprue cuts…do you see anything significant?
Top row…shiny round casts, they were cast @ 710*F. into a 6 cavity Lee mould that was running around 400*F. If they were dull, one or two things were the cause…lead pot @ 750*F. or hotter or the mould was too hot and I wasn’t giving it time to cool the heat I was pouring into it…my cadence/timing between pours was a little fast.
Second row, the sprue…the front of the mould was on the right side and the nearest cavity to me was the left side. Notice how the cavities have filled and started to run to your right? The cavity filled and the excess lead ran over the previously filled cavity…the lead did not run over into the empty cavity I intend to pour next. As soon as I see the lead back up in the sprue hole I am pushing the mould forward to begin filling the next cavity…I have not shut the pot spigot off, I run a continuous pour start to finish. This does two things…it gives the cavities plenty of lead on top of the sprue holes for the cooling cast to draw from, and because I had the mould tilted to the front it kept the lead from running into or splashing into the next cavity and giving a partial fill…that would cause the casts to have deep wrinkles because the mould cooled the spilled lead and then I poured on top of that…it looks terrible even though the cast is still shootable.
Third row, the base of the cast will tell you if you are cutting the sprue too soon or right on time. The left cast was cut ‘almost’ perfect…the right cast was cut too soon before the lead cooled and solidified…see the dark area from 11 to 12:00 on the sprue cut? That is a little void where the lead was pulled from the cast and went with the sprue…I opened/cut the sprue just 2 or 3 seconds too soon.
Fourth row, it shows where every cavity lost some lead by my opening the sprue too soon…notice the rough appearance of the cut? It should be smooth. The result of bad sprue cuts is a variance of the weight of your casts.
In the following picture you should now recognize what I just described in the picture above and ‘another thing’…this is where we should be looking every time we cut the sprue to see if the cut was good, meaning our cadence and timing is good also. The sprue cut is clean telling us that we gave the cast adequate time to cool from the sprue puddle down into the cast itself. The ‘other thing’ is, we get to see if the base of the cast if filled out to the edge of the cavity, these are fine but if they weren’t I would see a shadow around the circumference of the cast where it didn’t fill out completely, I would then know that I left too little lead on top of that cavity for the cast to draw from as it cooled…when it cools it shrinks and draws extra lead from the sprue puddle above, that keeps the cavity completely filled out nose to base.
In the next picture there are several things starting to go south. The closest and the farthest cavities did not fill completely and now you know what caused that. Most all the cavities have lost lead to the sprue cut…I opened/cut the sprue before the lead cooled into the base of the cast. Pretty simple forensics here…right? Something else you should notice is that the top of the mould has smears of lead on it, look at the closest cavity. That’s from my opening too soon and dragging melted lead across the top of the mould where it cools quickly and adheres. Keep a damp cotton washcloth near to wipe the mould before you dump this load of casts; that will usually pull the lead right off. If not, keep a little 3/4″ wide by 1/4″ piece of hardwood about the length of a ruler near to scrape the mould top…the wood won’t hurt the aluminum but it’ll push those smears off. Again, do that before you dump the casts.
The next picture shows some pretty casts, but there’s several things we can deduce from this picture. Look at the blemishes in the top right corner on the two casts laying sideways…what happened here? It could be that when I moved to the next cavity I didn’t hit the center of the sprue hole with the stream of lead from the spigot. That caused a little splattering of the lead as it entered the cavity. The splatter that entered cooled immediately forming those droplet looking blemishes and then the rest of the lead filled in around them. If this occurred at random I could be sure that is the cause of the blemish…but, if it’s forming on every cast coming out of that cavity I know that I have some lube oil from one of the mould pins or the sprue bolt that migrated into the cavity…it’s a gas blemish. The hot lead caused the oil to try to vaporize and it left a tiny blemish. These blemishes can get huge depending on how much oil got into the cavity…you must stop and clean the cavity with alcohol or brake cleaner or acetone on a swab. If it’s bad enough to be persistent you might have to cool the mould and boil the mould halves in detergent and rinse a couple times…re-lube the mould and start again.
Another thing you’ll notice is that there are shiny and dull casts…why? You’re right; I started with a 710*F. pot, didn’t watch the thermometer close enough, and the pot got hotter as it emptied and I started getting ‘frosty’ casts. The pot got hotter and made the mould get hotter, that made me have to wait longer between sprue cuts, and I started seeing smears like in the picture above. Things started going south and I wasn’t paying attention. This is not a problem, this is just an example of the details we can deduce from examining our work. Some of the fellas prefer frosty cast because the PC will adhere to them so much better…they claim.
Most of the sprue cuts are fine in this picture but…look at the bottom right corner. If I was watching, I would have detected that and slowed my cadence and checked the pot thermometer…instead I was prolly singing with the 60’s CD and sipping too much cold beer. The sprue cut was telling me that things were going south, but I didn’t see it.
If you look closely you’ll find some tiny ‘nicks’ or ‘cuts’…very short, there’s one on the top left side on that blemished cast…that is a mark from coming out of the cavity and bouncing off the other side of the mould…either I didn’t have the mould open enough to allow them to fall freely or I whacked it too hard with the mallet and that cast was propelled against the other side of the mould and bounced off it to the pan.
Ok, enough about some of the basics above…lets cast some Hollow Points. The mould below is my first SWC Keith style HP mould, an old Ideal from the mid 30’s, single cavity with a pair of removable pins….one deep (long) for the .357M, and one shorter for the .38S. Boys, at this point I had the above forensics figured out, but this mould was to take me to a new level of casting! It would challenge me to the point that I felt like a ‘newb’ again. A steel HP mould has to run hotter than the normal solid cast, and you have to keep that pin hot also…believe me, I had some pretty poor looking HP’s come out of this little fella.
The first problem was getting enough heat in the pot and in the mould and pin. I figured that 800*F. ought’a do it. Notice the smear of the sprue cut below…I was running too hot. Notice the small sprue puddle? That’s not a puddle in the normal sense…I was pressure pouring directly off the bottom of the spigot to make this mould fill out but with little success. Later you’ll see what pressure pouring off a bottom pour pot will give you…
Top row, the two on the right…yep, those are holes in the base of the cast directly under the sprue hole. Why? Because I didn’t pour a generous puddle for the cast to draw from as it cooled, it sucked air instead. Notice how the HP holes do not look round and even? Too hot again, the lead was trying to ‘fin’ down into the bottom of the mould where the pin comes through. Notice the bottom row second from the right….I didn’t always lock the pin correctly and it fell out as I went to pour the cavity…nuff said here huh?
With some help from some patient old timers I finally diagnosed all the problems…the biggest problem was getting the mould to the right temperature without overdoing it…the solution is the hot plate and 350~400*F. Notice the 3/4″ nut with the pin sitting nose down in it? That is to heat the pin so that I don’t get a blemish on the HP end of the cast like the bottom rightmost cast pictured above. Slowly my casting bench is starting to morph and take on a new look.
This is how I started, one 20# Lee pot elevated on top of a box with a thermometer I didn’t know was off by 45*F. . . . heck, it was a Dillon thermometer and I trusted it until I put it in hot boiling water and discovered it read low of 212*F. by the 45*…that could account for some of the frosty runs I made for sure! I made that mould whacker out of an end cut from a closet pole and thought that was a good idea before it started shedding splinters allover the bench. More things would change before I got to where I am today…
OK…here’s today, and I hope the ‘morphing’ of the bench is complete. The hot plate got an old tin can wired to the skill saw blade (the blade protects the mould from the red hot burner element, no warping of the mould halves) to make a mould ‘oven’ that would heat the entire mould, sprue plate included. When I’m in a run, I’ll turn the oven off, that’s why the thermometer on the oven is reading low. When I load the pot first thing I’ll put the mould in the oven and turn the temp up a wee bit past half way giving me about 400*F. in the oven…when the pot is ready, the mould is ready too and generally throwing good cast from the first opening. That thermometer is from the Home Depot BBQ department…cheap 600*F. thermometer.
The pot in the middle is my original, now it does regular pistol/rifle blends of lead because of the volume. It has a thermometer in this picture because I was learning how much delay there is in the thermometer versus the PID…the thermometer takes forever to rise and fall and you can’t depend on it to always know the lead pot’s temp. at any given moment, especially when you are putting sprue cuts back into the pot where you can see a 50* change almost instantly.
The little pot is for Hollow Point work, it never runs anything but 20~40:1 tin rich lead. The little stick is my mould scraper to get the pesky lead off the top of the mould. Notice how the mould is full and sitting on the base of the pot? I’ve gotten into the habit of using the base of the pot as a heat sink to allow me to run a faster cadence on the 6 cavities…I use it on the smaller moulds too but you really notice a difference where you are trying to cool a lot of heat.
Finally you see the PID control on the bottom left…all I can say about that is that I wonder why I didn’t get it sooner! In this picture I have the probe in a hole in the bottom of the big pot, just wanted to see what the offset would be, didn’t like this method so I’ve now gone to placing it in the top right in the lead near the spigot…it will run either pot and I can control the heat between 690* and 750*F. by simply changing the desired target temperature on the PID…simplicity! Someone noticed I said 690* when I’ve been saying 710*…sharp eyes! Today I was experimenting to see whether I could get ‘shinier casts’ with even cooler lead…didn’t notice any difference except that the spigot froze up a few times and I went back to the old stand-by of 710*F.
Last but not least, you notice the PVC pipe I screwed onto the wood mallet? That put an end to all the splinters getting into everything!
So…there you go Boys…some comments and pictures of the basic things to learn about casting and diagnosing your work on the fly. From what we have talked about here there’s prolly 10 times more we could have discovered. Perhaps we will go into the technical end of the lead blends, the how’s and whys of the lead matrix, the importance of tin (Sn) and antimony (Sb) and arsenic (As) as time permits in the future, and depending on the comments and questions posted below that show enough interest.
Until then, and for those who can’t wait, there’s a website that has everything you could possibly know about casting. One of my favorite reads is…‘From Ingot to Target: A Cast Bullet Guide for Hangunners’ found here at LASC > http://www.lasc.us .
“Good luck out there Boys…take it easy, be careful…don’t hurt yourselves!”
c h a r l i e
Born in 1950…HS grad, some college, no degrees, served in the US Marine Corps, educated there by the Navy in Electronics. Worked as an Electrician all my life and Contracted Heavy Industrial Control & Power Distribution for 20 years before retirement. Drive a black Chevy 4×4 and a Harley V-Rod. Married 40+ years, 3 great kids all 45 & older. Love my shop & do it all right there…