Mould temp and cast size?

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Had some time to cast with a 460483 378Gr. RN mould
This has been a great bullet and a fun one to load and shoot
Preheated mould to about 280F and cast one pour.
Discarded first pour.
Cast two more pour’s at 280F to 295F
Measured all ten:
.46025
.46020
.46040
.46035
.46040
.46020
.46050
.46070
.46035
.46045

Ran mould temperature up to 340F to 360F and got frosty bullets
Cast two more pour’s
Measured all ten:
.45960
.45980
.46005
.45985
.45970
.45970
.45940
.45920
.45890
.45860

Temperature differences are a lot more apparent in a bigger bullet
Just something to ponder

Bullet maker, maker
Al Nelson

Topic

[cliftonmorris]

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Lots of interesting testing going on here.  Has anyone worked with the pouring order of the cavities? I have noticed that I seem to get better results on 4-6 cavity moulds if I alternate which end I fill the mould from. Better quality fills. The alloy I have been using most recently is basically half and half pure lead to Rotometal’s hardball alloy. As I understand it this should be about like Lyman #2.

[adamsutherlandModerator]

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A little bit more on cavity size in relation to temperature.

http://www.castpics.net/subsite2/GeneralReference/CavitySizeVsTemp.pdf

[petergallo]

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Lots of interesting testing going on here.  Has anyone worked with the pouring order of the cavities? I have noticed that I seem to get better results on 4-6 cavity moulds if I alternate which end I fill the mould from. Better quality fills. The alloy I have been using most recently is basically half and half pure lead to Rotometal’s hardball alloy. As I understand it this should be about like Lyman #2.

I do the same thing, changing which end gets filled first.  It does seem to help keep cavity temps more even.

Did you try to loosen the sprue plate on the problem mold?  It’s contrary to what you would think but sometimes it helps.

[cliftonmorris]

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No I didn’t. I thought surfacing it would be best. Now that you mention it I have a L brand mold that the plate is so loose on it flops Around and it casts great bases.  I’ll give that a try.  I just cast 10 lbs of the best .45 #68 s I’ve ever cast. Thank you all for the great info available here.

[jameswilson]

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Monday i went out and cast some more 325 grain fp for the 45-70.
Did the lower temp thing going down a little at a time.
Stopped at 650.
When compared to the batch i cast the week before they measured larger in diameter and they were not lopsided.

Just goes to show you that you can always learn to do things differently.

Thanks for the tips.

[petergallo]

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That’s a great point.  Heavy bullets often cast well with a lower pot temp than itty bitty ones.  I wave cast a bunch of 300’s and it’s different than the 90 grain 380acp bullets.  The big ones seem to get the mold hotter, even at a lower pot temp.  It’s not one size fits all.

[anthonylafleurParticipant]

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When desiring the largest diameter from any mould with a given alloy I use as cool a lead temp as possible, but cast rapidly to keep mould temps as high as possible. The cooler temp melt will shrink less, while the hottest mould will be expanded as much as possible.
The opposite is true for wanting a smaller diameter…hotter melt and cooler mould blocks. The use of water-quenching the mould blocks, or resting them on a sponge (or folded wet towel) can be very effective at keeping mould temps as low as possible. Careful quenching can also help control the occasional hotspots that appear as frosting in areas that measure significantly smaller, and out of round, than the rest of the bullet. 

[cliftonmorris]

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I got my new NOE 452-230rg(small) out for its first runs. This is my fist use of a mold thermometer and it seems to help quite a bit. I was using an alloy of 3 lbs pure lead to 1 lb of Rotometal hardball alloy. I also started using a hot plate to get the molds up to temp before casting.  460 on the mold and 700 on the lead pot seems to give best results. Well filled bullets with no frosting. Nice sharp edges on the base and you can see the surfacing mill marks from the spruce plate on the base.  I experimented some with technique. Using the pots bottom pour I just wasn’t getting good bullets. I found lots of little splash pockets at the lube grooves and the hollow point didn’t form as well. I switched to an RCBS ladle and things were a bit better but every now and again I was getting a bullet (1 out of the four cavities) that would have rounded edges at the base. I tried a new bottom pour feed ladle that I got from Rotometals and that baby would allow good control of how fast the mold filled. If I flooded the cavities quickly and had a nice molten puddle on top of the sprue plate I found I had time to put down the ladle and pick up the mold mallet and tap the mold handles lightly before the sprue would solidify. This seemed to give the best bullets with the least culls overall.  I’ve been thinking about grinding a bit of a trough between the countersinks of the sprue plate to see if that will  hold the lead closer to the sprue  and make filling the cavities quickly a little less tedious.  I found that if I tip the mould to the left, with the clips for the hollow point pins down and tapped the handle to open the mold, the bullets all tended to drop out of the top half and then tipping the mold back to the right would get them to drop out and off of the pins without distorting the hollow points.  I let the mold cool to 465 before making another pour and these look like the best quality bullets I’ve cast to date. Very consistent

[lwatsonParticipant]

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Kwixdraw – interesting addition to a fascinating thread.

I too was getting splash pockets indentations using a bottom-pour (with both of my Lee & Lyman furnaces) right above the top driving band.  Fast-flow or trickle, it made no difference, too many just came out bad and looked bad. So I went to a dipper, and use a slowly tilting pour from canted-right 45 degrees, slowly tilting to upright as I slow-pour into the mold, I sort of visualize the cavity-air as needing time to escape..as if I was pouring expensive Scotch liquor into a narrow mouthed hip flask…  result, never see a splash pocket, even with just-warm molds and cool melt. And the bases rarely show any frosting at any temp combination.

I found sharp spitzers, like my new 311414, did not like a fast pour from dipper, the slow tilt and pour above and all are good, razor sharp and perfect.  Only downside, I can’t cast fast as I want, but the end results are great.

Thanks all for the data on temps affecting final sizes.  I need to start experimenting with mold and melt temps more, to get some of my treasured antique molds dropping a bit fatter at last.

[cliftonmorris]

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Another technique for those molds that fight you for that last driving band at the base. I have a cast iron mold from R**S that casts a .45 cal., 185 gr SWC. The thing has a bevel base and will rarely cast anything usable unless you coax it a bit. The bullets tend to have mis formed bases and sometimes the driving bands don’t want to fill out either. The bases will frost and still not fill out to form the bevel. I tried turning the mold upside down and shaking it. Nothing seemed to matter. Finally I cleaned the mold with some plain old white vinegar. Scrubbed it with a cue tip and washed that off with rubbing alcohol. After getting the mold good and clean I started getting a few good bullets are the mold came up to temp but one I started casting faster the bases frosted and deformed again. I started tipping the mold so the metal flowed in on the side of the cavity and as I rolled the mold upright I increased the flow and the height above the mold to the ladle. As I finished the pour I let the excess metal run off the spre plate until there was just a smear and a bead in the bottom of the funnels. That metal cooled almost instantly and could be cut off right away. This seems to form perfect bases very regularly. My theory is that having just a small amount of cooling metal on the sprue plate makes it shrink less than having a large blob of hot metal sitting up on top that might shrink enough to pull metal back out of the mold and deform the base before it solidifies. Something to try if you have a mold with problematic bases.

[Author]

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