357shooter
02-26-2011, 05:13 PM
OK, several folks here convinced me to do further testing. This time it's all about mould temps.
It's worth stating again: I cast exclusively for 357 Magnum. So some results from my testing may be helpful, but maybe not. :bigsmyl2::bigsmyl2:
I was able to use the NOE Digital Casting Thermometer to keep all temperature measurements right on the money.
Note, this an important point: the test results must be adapted to be effective during a casting session.
Also, my test alloy is 98% lead and 2% solder, which likes things hot.
When preheating the mould (hot plate or dipping into the alloy) the cavity temperature is approx 80 degrees cooler than the mould block itself. The temps in the charts during the test are mould block temps, the cavity is a little cooler. I decided to be consistent and report what the actual mould temps are during testing. I will explain how to adapt for a casting session in just a minute
First, the test process for my test mould (358-429 aluminum 5 cavity);
Preheat the mould to the desired test temperate by heating it on a hotplate. As the temps increased it had to be dipped it into the alloy to produce the hotter temps. The cavity temp is consistently 80 degrees cooler both ways, so the results are consistent.
The results are in following three separate charts:
1. Bullet diameter measured on the casting seam
2. Bullet diameter measured 90 degrees across the seam (cross)
3. The difference between the two diameters or the amount the bullet is out of round
The diameters measured on the seam (big is best):
http://i878.photobucket.com/albums/ab341/prgallo/Mouldtemptest-seam.png
The diameters measured across the seam (big is best):
http://i878.photobucket.com/albums/ab341/prgallo/Mouldtemptest-cross.png
The amount “out of round” (small is best):
http://i878.photobucket.com/albums/ab341/prgallo/Mouldtemptest-round.png
The best bullets, the biggest and most round, result from a mould preheated to 540 degrees. That puts the cavity right at 460 degrees. Then the roundness and overall size falls off quickly.
The window for the absolute best result is very narrow. That can be a challenge. Maintaining the optimum temp by feel and experience is good, but not the best solution. I've started to use the Digital Casting Thermometer all the time, because it works well. It's all about great results.
Now, how does this work in a real casting session. It turns out that while casting, the heat is now coming from the cavity instead of outside the cavity. The cavity and mould temp are now much closer to each other.
With that in mind, keeping the mould between 510 and 520 produces absolutely terrific bullets. They are very round, as good as the best test results, full sized too. Some early signs of frosting may show, without impacting bullet quality at all.
Heating the mould hotter than 520 degrees produces frosted bullets and the results are not as round and are not fully sized.
I found it was hard to keep the mould up to 520 degrees, luckily it didn’t need to be hotter. At 520 degrees the squared grooves in the bullet design make it a bit tricky to get them to drop, but a couple of taps shakes them loose.
The best solution proved to be; preheat to 530, using the Digital Casting Thermometer from NOE, and then pace the casting so the mould temp maintains 510-520 degrees. The bullets and mould are into their “sticky” area at these temps, backing down a bit to 500-515 may help and won’t hurt the results.
Now to see what the "sweet spot" is on other moulds. Also time to shoot some of these great bullets in my new Rossi 357 lever rifle.
It's worth stating again: I cast exclusively for 357 Magnum. So some results from my testing may be helpful, but maybe not. :bigsmyl2::bigsmyl2:
I was able to use the NOE Digital Casting Thermometer to keep all temperature measurements right on the money.
Note, this an important point: the test results must be adapted to be effective during a casting session.
Also, my test alloy is 98% lead and 2% solder, which likes things hot.
When preheating the mould (hot plate or dipping into the alloy) the cavity temperature is approx 80 degrees cooler than the mould block itself. The temps in the charts during the test are mould block temps, the cavity is a little cooler. I decided to be consistent and report what the actual mould temps are during testing. I will explain how to adapt for a casting session in just a minute
First, the test process for my test mould (358-429 aluminum 5 cavity);
Preheat the mould to the desired test temperate by heating it on a hotplate. As the temps increased it had to be dipped it into the alloy to produce the hotter temps. The cavity temp is consistently 80 degrees cooler both ways, so the results are consistent.
The results are in following three separate charts:
1. Bullet diameter measured on the casting seam
2. Bullet diameter measured 90 degrees across the seam (cross)
3. The difference between the two diameters or the amount the bullet is out of round
The diameters measured on the seam (big is best):
http://i878.photobucket.com/albums/ab341/prgallo/Mouldtemptest-seam.png
The diameters measured across the seam (big is best):
http://i878.photobucket.com/albums/ab341/prgallo/Mouldtemptest-cross.png
The amount “out of round” (small is best):
http://i878.photobucket.com/albums/ab341/prgallo/Mouldtemptest-round.png
The best bullets, the biggest and most round, result from a mould preheated to 540 degrees. That puts the cavity right at 460 degrees. Then the roundness and overall size falls off quickly.
The window for the absolute best result is very narrow. That can be a challenge. Maintaining the optimum temp by feel and experience is good, but not the best solution. I've started to use the Digital Casting Thermometer all the time, because it works well. It's all about great results.
Now, how does this work in a real casting session. It turns out that while casting, the heat is now coming from the cavity instead of outside the cavity. The cavity and mould temp are now much closer to each other.
With that in mind, keeping the mould between 510 and 520 produces absolutely terrific bullets. They are very round, as good as the best test results, full sized too. Some early signs of frosting may show, without impacting bullet quality at all.
Heating the mould hotter than 520 degrees produces frosted bullets and the results are not as round and are not fully sized.
I found it was hard to keep the mould up to 520 degrees, luckily it didn’t need to be hotter. At 520 degrees the squared grooves in the bullet design make it a bit tricky to get them to drop, but a couple of taps shakes them loose.
The best solution proved to be; preheat to 530, using the Digital Casting Thermometer from NOE, and then pace the casting so the mould temp maintains 510-520 degrees. The bullets and mould are into their “sticky” area at these temps, backing down a bit to 500-515 may help and won’t hurt the results.
Now to see what the "sweet spot" is on other moulds. Also time to shoot some of these great bullets in my new Rossi 357 lever rifle.