Different Casting Temps & BHN

[lv2tinker]

Different Casting Temp and Water Drop BHN

As a “new” caster, this is my first real posting here.
Got bored the other day and thought I would try casting boolits at different Temps, water dropping them and checking the BHN within 6 hrs, and after 48 hrs just to see what the difference was.
I used a .41 cal LEE TL-410-210-SWC double cavity mold that I bought at a swap meet for $10. (Didn’t need it as I don’t have a .41 Mag but just couldn’t resist). 
My BHN tester is a homemade rig using an RCBS Rock Chucker Jr. press, a Daisy Rider BB, a digital caliper, a “strong” magnifying glass and a 20 lb weight: http://www.mountainmolds.com/bhn.htm I used this Brinell Hardness Number Calculator: http://www.gordonengland.co.uk/hardness/brinell.htm so the actual BHN numbers may or my NOT be accurate, (they look a little high for W-W’s) but the numbers will work for this “comparison” test. (Also added 12" 95/5 lead free solder to the mix).
I used the dial Temp # on the 20 lb RCBS bottom pour pot. (Don’t have a thermometer yet). Whenever I do get one, I’ll append these temp # to show actual #’s.
Fluxed and stirred real good between temp tests. (15 min.) Started at 700deg and worked my way up.

Pot
Temp 6 hrs 48 hrs Diff.
700 Would not pour.
725 16.3 20.3 +4.0
750 16.3 21.5 +5.2
775 18.0 21.5 +3.5
800 19.2 24.0 +4.8
825 20.3 24.2 +3.9
850 20.3 24.2 +3.9

This test was a real eye opener for me.

-al

[VTDW]

Welcome aboard. From your writing is looks as though you have what it takes to be successful in this new endeavour of yours and should excel at it.

Dave

[MT Gianni]

Welcome. What kind of thermometer did you use to measure temps with? You should flow with most alloys at 700. Gianni

[dubber123]

Neat way to test. Your BHN #'s of 24.2 at your max heat test match pretty close to what I get on an LBT tester, so at least at that setting, your rig looks pretty accurate. Welcome aboard.

[jack19512]

What kind of thermometer did you use to measure temps with?





"I used the dial Temp # on the 20 lb RCBS bottom pour pot. (Don’t have a thermometer yet). "

[Bass Ackward]

Temp 6 hrs 48 hrs Diff.
700 Would not pour.
725 16.3 20.3 +4.0
750 16.3 21.5 +5.2
775 18.0 21.5 +3.5
800 19.2 24.0 +4.8
825 20.3 24.2 +3.9
850 20.3 24.2 +3.9

This test was a real eye opener for me.

-al


Well Al, This won't be the last eye opener either. Wait until you mold a batch that don't appear to be hardening. You get discussed or distracted and come back two weeks later and they turn out harder than what you did before. Same with HT in an oven. You can control final hardness to a degree by temperature and your speed to the quench which is temperature again. Change bullet diameter so the bullet cools faster or slower and everything changes again. Change percentage of antimony and all numbers change again.

So don't trust linearity in your load calculations, always measure or wait the required time before use.

[Andy_P]

Is this new, or has this theory been tested before and published?

- can we say that the higher the casting temperature the harder the bullet?
- just when water dropped?
- is it the alloy-water temp differential that causes the increased hardness or just the casting temp?
- what about varying the water temp (ice-water, tap-temp, room-temp, hot water)?

There are many variables of course, and the test was perhaps not "scientific" (inaccurate temperatures, inaccurate BHN readings, too few tests, etc.), but it is very interesting.

[Harry O]

Of course, cooling speed makes a big difference, too. Not just water quenching vs towel drop either. I have a mix I use for a lot of calibers I shoot. It is one pound of WW, 1-1/2 pounds of pure lead, and 1/2 oz of pure tin. A very economical mix.

I air drop all bullets into a dry towel. With 100gr bullets, it gives a Bhn of 9.5 to 10. With 200gr bullets, it gives a Bhn of 9. With 400gr bullets it gives a Bhn of 8 to 8.5. The larger the bullet, the slower it cools and the softer it is.

[lv2tinker]

Thanks to everyone for your welcomes, replies/comments & imput.
I haden't seen any other posts about Temp/BHN correlation, that's why I tested this out. Hopefully, it will be a help/general guide for other newbie’s here on the board. And I'm looking forward to "more eye openers" as this is an interesting & enjoyable 'hobby'.

[lv2tinker]

Andy_P
Good questions. I had these same questions in mind when I started this test.
- Is this new, or has this theory been tested before and published?
Hadn't seen it anywhere here, that's why I posted my results.
- can we say that the higher the casting temperature the harder the bullet?
Only when it is water droped or oven Heat Treated.
- just when water dropped?
Yes, or when HT.
- is it the alloy-water temp differential that causes the increased hardness or just the casting temp?
In my limited experience, both.
- what about varying the water temp (ice-water, tap-temp, room-temp, hot water)?
I wouldn't think that it would make "that" much difference. I used cold tap water.
There are many variables of course, and the test was perhaps not "scientific" (inaccurate temperatures, inaccurate BHN readings, too few tests, etc.), but it is very interesting.[/QUOTE]

Thanks,
-al

[lv2tinker]

Of course, cooling speed makes a big difference, too. Not just water quenching vs towel drop either. I have a mix I use for a lot of calibers I shoot. It is one pound of WW, 1-1/2 pounds of pure lead, and 1/2 oz of pure tin. A very economical mix.

I air drop all bullets into a dry towel. With 100gr bullets, it gives a Bhn of 9.5 to 10. With 200gr bullets, it gives a Bhn of 9. With 400gr bullets it gives a Bhn of 8 to 8.5. The larger the bullet, the slower it cools and the softer it is.

What are you shooting these 'soft' boolets in?
I'm shooting mine in 9mm,(18 BHN) .40 S&W (18 BHN) and .45 ACP (11 BHN). As a new caster, I'm using LEE's pressure/BHN chart as a guide.

-al

[MT Gianni]

In Veral Smith's book he says water temp makes a big difference. Ice water vs 55 degree tap water. Gianni

[felix]

If you use big diameter boolits, the water temp makes a difference. The rate of temp change of the slug makes for the potential hardness, but once below 300 degrees there will be no further change. For example, a 22 boolit will get to 300 degrees very fast, either water dropped or air dropped, so water temp has very little bearing, if any, on the final hardness. Contrast that with a 45-70 boolit. ... felix

Ideally, you want a "water" that does not boil at 850 (more like 550) degrees. The generated "air" around the boolit detracts from the rate of change because of the insulation of the air.

Because of the 300 degree demarcation, you can take the boolits out of the water and place them back into an oven at say 200 degrees for several hours. This will cut the hardening time dramatically. The boolits will make maximum hardness within the time in the oven.

... felix