An interesting simple casting experiment

[texasmac]

I knew that the alloy temperature affected bullet weight but had never determined how much. Normally I went with the temp that resulted in fully filled out bullets using a specific alloy. Since I planned to cast sufficient bullets for 3 silhouette matches I figured I’d run a simple experiment. So I just finished casting & weighing 3 batches (60 bullets/batch) of .40cal 400gr bullets using the BACO 409400M5 (old 409400M4) mould and the RCBS Easy Melt PID controlled furnace.

The 1st batch was cast at 765 degrees & weighed 400.0grs +/- 0.6grs. The alloy temp. was increased to 770 degrees for the 2nd batch which weighed 401.0grs +/- 0.3grs. So then I lowered the alloy temp. back to 765 degrees for the 3rd batch with dropped back down to the same weight as the 1st batch (in this case the weight was 400.0grs +/- 0.5grs). So now I know that 5 degrees will result in a change of approximately 1gr.

BTW, the alloy was verified as 15.7:1 by measuring the specific gravity using a laboratory grade high precision scale.

Wayne

[country gent]

Interesting. I thought it would take more of a temp change to affect weight.

[greenjoytj]

Texasmac:
The weight of your bullets changed slightly with a change in casting temperature.
What did the changes in casting temperature do to the bullets diameter?
I suspect the bullets cast hotter will be slightly smaller in diameter but by how much compared to the cooler cast bullets?

[texasmac]

Texasmac:
The weight of your bullets changed slightly with a change in casting temperature.
What did the changes in casting temperature do to the bullets diameter?
I suspect the bullets cast hotter will be slightly smaller in diameter but by how much compared to the cooler cast bullets?

Since a hotter alloy results in a hotter mould which will increase the mould dimensions a miniscule amount, the bullet will be larger overall by a miniscule amount. In this case a 1gr increase is only 0.25% of the total weight of 400grs & the resulting diameter change is way too small to be detectable by any measuring device I have. Keep in mind that the weight variance within each batch is equal to or slightly more than the increase in weight due to the temp. increase.

Wayne

[EDG]

The 1 gr delta out of 400 grains is a change of only .25% - not very significant.

If you weigh and graph each bullet in the order it was cast you may find a trend as the mold gets hotter.
There is also the possibility of a trend related to falling head pressure as the metal level in the pot drops.
Even if there is no trend you can still graph the variability of the bullets and throw out the highs and lows- at least the lows which may be more frequent.
I would expect more variability at the bottom end of the weight distribution since it is possible to cast bullets that weigh less or even a lot less if you make a mistake pouring. Some of the variability can be due to gas inclusions too.
However when the mold is correctly closed the top end of the distribution should have an upper limit. When the mold is closed properly with nothing between the blocks the volume of the cavity is finite and the maximum weight should approach some asymptote.

[texasmac]

The 1 gr delta out of 400 grains is a change of only .25% - not very significant.

If you weigh and graph each bullet in the order it was cast you may find a trend as the mold gets hotter.
There is also the possibility of a trend related to falling head pressure as the metal level in the pot drops.
Even if there is no trend you can still graph the variability of the bullets and throw out the highs and lows- at least the lows which may be more frequent.
I would expect more variability at the bottom end of the weight distribution since it is possible to cast bullets that weigh less or even a lot less if you make a mistake pouring. Some of the variability can be due to gas inclusions too.
However when the mold is correctly closed the top end of the distribution should have an upper limit. When the mold is closed properly with nothing between the blocks the volume of the cavity is finite and the maximum weight should approach some asymptote.

Ed,

Although the average 1gr change due to a 5 degree alloy temp change was easily determined by weighing each bullet, I certainly agree that it’s not very significant. BTW, I use locking mould handles so the mould is always closed with the same amount of pressure. I also keep a very consistent cadence, rarely make a pouring mistake when casting & preheat the mould with a separate laboratory hot plate. When weighing and plotting each bullet as cast, which I do after each casting session, the widest variation tends to be at the low end of the weight distribution curve which I believe is the result of voids in the bullets and, to some degree, caused by the initial instability of the mould temp.

Preheating the mould to about 460 degrees F eliminates most of the need to reject the initial lower weight bullets due to a “cold” mould, but a few will still vary a greater amount from the average weight until the mould temp. settles down due to the cadence.

Wayne

[EDG]

You have some interesting data.
I have seen a lot of techniques used in industry to insure top quality castings.
I wish they were not so expensive because I would like to try a few of them.
One of them would be to automate a Magma Master Caster and put the whole thing in a vacuum chamber.
I am curious to see if you can get rid of internal voids when there is little atmosphere. Having the entire pot in the vacuum will cause any gas in the molten metal to expand and rise to the top of the melt much faster so there is little gas in the metal that is poured into the mold.

[texasmac]

You have some interesting data.
I have seen a lot of techniques used in industry to insure top quality castings.
I wish they were not so expensive because I would like to try a few of them.
One of them would be to automate a Magma Master Caster and put the whole thing in a vacuum chamber.
I am curious to see if you can get rid of internal voids when there is little atmosphere. Having the entire pot in the vacuum will cause any gas in the molten metal to expand and rise to the top of the melt much faster so there is little gas in the metal that is poured into the mold.

Ed,

Due to the density, weight & heat of lead I doubt there's any gas or trapped air in the pot alloy. I believe any voids in the bullets are induced while the alloy is being poured into the mould. Of course I have no way of verifying either. But having used vacuum chambers for several applications including eliminating gas & air pockets in various types of plastic castings for the technology industry I'm betting your vacuum casting approach would work if only to remove any voids while filling the mould.

Wayne

[Chill Wills]

I would think ....IF one could cast in a vacuum, there would be little to no oxidation and given clean metal to start, the castings should produce very little in the way of inclusions. I believe most inclusions are lead oxides.

[country gent]

Chill Willis,
Most industrial casting machines ( die cast, injection molded and plastic ) cast under heavy pressures generated with a shot tube. This tube holds a little more material than the die does and literally pushes it into the mould Filling the mould and channels completely. This made the materials grain structure and strength much better. When poured in a can or mould with no pressure it was soft and gummy loaded tools and deformed easily. The parts cast under pressure were much more machinable and durable. Casting under pressure with lead might make a better bullets just from the grain restructuring and better fill. We poured rubber parts ( polyurethane) also. material was vacuumed several times to remove air then poured on the mould and cured in a pressure vessel at 100 psi. Again this affected the surface finish and hardness of the parts, durometer was harder when cured under pressure.

[Chill Wills]

I would think ....IF one could cast in a vacuum, there would be little to no oxidation and given clean metal to start, the castings should produce very little in the way of inclusions. I believe most inclusions are lead oxides.

Hey Country Gent, I think I did not write clearly enough or you did not understand the Vacuum reference. I was not talking about pressure casting using atmospheric pressure to drive the fluid, - although EDG was.

I just meant that in the absence of oxygen, a vacuum, lead oxides would not form on the surface and make their way into the finished product.
Not a likely casting scenario here on earth - until we start casting in space or on the moon.

[country gent]

You can purge the surface of oxygen with a layer of sawdust or charcoal that smolders or wax that seals the surface. If you have a gas flux welder the argon flux could be metered over the pot also. In the food plant I worked, We welded thin wall stainless steel product pipes like this a disc with small hole was taped to one end and a disc with hose on other weld the tubing joint. No flash or cud inside inner surface as a smooth bead. If your casting bottom pour a cover with a hose fitting and a small vent hole Tank of argon and meter to maintain gas level. So it is doable to cast inn a oxygen free pot.
And yes I did misinterpret your meaning of the vacuums use.

[Chill Wills]

You can purge the surface of oxygen with a layer of sawdust or charcoal that smolders or wax that seals the surface. If you have a gas flux welder the argon flux could be metered over the pot also.
No flash or cud inside inner surface as a smooth bead. If your casting bottom pour a cover with a hose fitting and a small vent hole Tank of argon and meter to maintain gas level. So it is doable to cast inn a oxygen free pot.
And yes I did misinterpret your meaning of the vacuums use.

Right.


It is really a non issue for me. I ladle pour, and pretty much cast great bullets on demand.
Any issues I have with accuracy are due to other problem sets and not so easily addressed.
For instance, too many birthdays. Cataracts. An inferior lot of fluffy Swiss powder.

If the quality of my bullets was the limiting factor on my scores, I would win every match.

[Lead pot]

I have cut and turned a lot of bullets on a lathe that were light weight but looked good with out flaws on the outside and I have never found a bullet with a clean airspace bubble inside. I always found dross that got poured into the mould.
I eliminated this problem by wiping some wax on the ladle spigot and putting a small chip inside of the ladle every 10 pours or when the dross started to stick on the spigot again. Keep the ladle clean and back drag the ladle filling it and your weight differential will drop and your bullets will be match quality.

[country gent]

My pot for casting is a cut off propane tank, I insert the ladle to the bottom make a swirl around the pot and raise out full. I found the swirl helps keep the ladle clear and the alloy mixed. One of the reasons for the bigger pot is do to my health issues ( mobility problems, numbness, ) when I cast a couple friends come over and we all sit around the pot and cast bullets and visit. THey are older and have some issues so were all together may not stop an accident but there is someone there to help and get help if needed.
I do open the spouts on my ladles to around .200 and lightly polish them inside and out, not a mirror polish but just smooth out the cast surface with a brush and valve grinding compound on a dremil tool.