Different HArdness from the same batch

[Irascible]

I recently cast 2 sets of bullets on the same day. RCBS 2 cavity 210gr PB 41 Mag and Lyman 215gr 429215 GC 44mag in 4 cavity mould, all where cast from Lyman#2 made from WW and 50/50 solder at 650 degrees and air cooled. After 10 days, the avg hardness of the 44 bullets is 15BNH and the 41 bullets is 20. No metal was added, but sprue was re added after the 41 bullets and the mix was re-fluxed. Why the difference? I repeated the excercise the following day and received the same results?

[felix]

41 boolits are smaller than 44 boolits, so will cool at a faster rate. ... felix

[runfiverun]

did you flux the mix in or scrape the oxides [ sb-sn] off the top
taking out a big spoonfull of oatmeal
is abit of them in a 10 or 20 lb pot.
plus what felix said think water quench with air

[Marlin Junky]

How many samples did you test for hardness? 650F is an awful low casting temp and you may have voids, especially in the bigger boolits.

MJ

[grumpy one]

I recently cast 2 sets of bullets on the same day. RCBS 2 cavity 210gr PB 41 Mag and Lyman 215gr 429215 GC 44mag in 4 cavity mould, all where cast from Lyman#2 made from WW and 50/50 solder at 650 degrees and air cooled. After 10 days, the avg hardness of the 44 bullets is 15BNH and the 41 bullets is 20. Why the difference?

I think the most likely cause is differences in mould temperature, especially since the harder bullets came from the much more massive RCBS mould.

To give an example, I cast a series of Lyman 311291 bullets in a 2 cavity mould, and a series of Lee C-309-170F bullets in a single cavity aluminium mould, using the same pot of alloy at the same temperature on the same day, and air cooling all the bullets in the same way. I then separated the shiny-cast 311291 bullets, made while the mould was warming up, but after tossing out all the imperfect bullets made too early in the mould warm-up process. There were five shiny 311291, which I compared with five frosty C-309-170F four weeks after casting. The shiny 311291 averaged 24.5 BHN (standard deviation 4.9), and the frosty C-309-170F averaged 13.6 BHN (standard deviation 1.9). I also found that the iron DC Lyman mould took much longer to warm up than the aluminium SC Lee mould.

My explanation of these results is that the shiny 311291 bullets were quenched by the relatively cool mould. The frosty C-309-170F bullets were not quenched by the light aluminium mould - in fact I had to cool the Lee mould against a wet rag between casts, or it took way too long for the sprue to harden.

[NSP64]

My explanation of these results is that the shiny 311291 bullets were quenched by the relatively cool mould. The frosty C-309-170F bullets were not quenched by the light aluminium mould - in fact I had to cool the Lee mould against a wet rag between casts, or it took way too long for the sprue to harden.
Good theory. Have you tested the Lyman's that were cast with the mold warmed up,against the Lee's. If both were frosty then the BHN should be the same. If it is the same, you Proved your theory.

[Shuz]

Here's something to try--Take a samples of both boolits and heat them in an oven to 475deg and then immediately water drop them. I'll bet the hardnesses are a lot closer!--Shuz

[Irascible]

Thanks for the theories, but I don't see an applicable reason.
The Lyman 44 mold was the more massive.
The bullets, although one is .020 smaller in diameter, weigh about the same.
No new metal was added.
The hardness was tested on 5 samples of each and averaged.
All in all it's still an unsolved mystery!

[Marlin Junky]

You'll have to solve your own mystery, we're just providing the clues. The answer lies within the chemistry of the solidifying lead. I don't think 650F is a good temp to be casting in the first place. I have tried casting at temps below 700F with a ladle and produced large standard deviations in bullet weight which means internal voids assuming the cavity fill-out is normal from bullet to bullet.

MJ

[grumpy one]

Good theory. Have you tested the Lyman's that were cast with the mold warmed up,against the Lee's. If both were frosty then the BHN should be the same. If it is the same, you Proved your theory.

I like your experiment, but had to vary it slightly since it's now three months later. However I still had the bullets cast in the original session, aged-up by three months. It turned out to be emotionally painful: I had plenty of 311291 frosty culls, but no C-309-170F culls; that little mould works well since leementing. I had to sacrifice ten perfectly good C-309-170Fs - the pain, the pain!

Results were:
Ten 311291, all frosty, at three months: Mean BHN 14.8, standard deviation 3.1
Ten C-309-170F, all frosty, at three months: Mean BHN 14.2, standard deviation 2.4

My interpretation of those results is that they are consistent with my prior hypothesis, that mould temperature has an important effect on bullet hardness, and the mould tends to quench the bullets unless casting in the frosty temperature range. The new data also suggest that I tend to cast at a slightly higher temperature with the SC Lee compared with the DC Lyman, but it isn't a totally fair comparison because the Lymans were culls and the Lees were perfect; there may potentially have been some temperature difference between Lyman culls and perfects, even though all were frosty.