Getting Hard

[ColColt]

I cast a couple hundred 44 cal bullets this afternoon and decided to check the BHN after the first 50 had cooled and they were about 11-11.5. Some hours later I checked again wondering if I had correctly measured the first ones and they turned out to be 12.5. Is that possible? For them to harden in less than 24 hours by one BHN number seems out of the ordinary. The actual numbers, according to the Lee tester were originally .068, which is 11.0, and then some hours alter .064(12.5).

[felix]

Yes, probable with a high antimony/tin ratio. ... felix

[onondaga]

Yes, save one to check in 7 -10 days, they will be stable then. Seven day hardness is typically a standard, but I'm not sure there is a fixed rule.

Actually, using the Lee, at a 20 or 40 second hold instead of a 30 second hold will easily show the size differences you are seeing; so use a watch if you aren't and stick with the 30 second hold the Lee is designed for. The longer the hold, the more the metal will flow from the indenter.

I have the Lee and am very happy with it.

Gary

[geargnasher]

Timing is essential, but after 30 seconds with most boolit alloys (containing antimony) I can't tell that the indention gets any bigger. With low-tin lead alloy, like 50:1, the lead just keeps spreading after 30 seconds, and it's quite noticeable.

Gear

[cbrick]

Sure it's possible. It's the antimony percentage that controls this. A low antimony alloy, say under 2%, will still age harden or HT but the aging time curve will be longer. Antinomy at 3-6% will age harden or HT quicker. Having the tin percentage higher than the Sb percentage can also play a role. And as was mentioned, operator error with the tester can also introduce variation, consitencey is the key.

Rick

[ColColt]

I never considered timing a factor at all. I just wait until the spruce gets hard, witnessed by turning gray, and then cut the spruce, wait a bit-maybe five seconds or twenty, I don' keep count and open the blocks.

The alloy was lead mixed with 50/50 lead to Linotype since I had a fair amount of ingots that were 50/50 I decided to use those along with a quantity of lead to soften it. Normally, the 50/50 is around BHN 14-15 that I have and so wanted to go to 10-12 for lower velocity rounds. The lead was in bars and pretty soft at BHN7.5 so, I knew it had other trace material in it but you could cut it with the thumbnail and feel the indent. When I measured it for softness that was the number.

I'm within the specs of what I wanted so all is well there just curious about the change in hardness. I measured this morning just due to curiosity and found that particular batch was on average, and if I held my hand steady enough with the Lee tester, BHN11. I'll check again for the heck of it next week and see if there's any further change. I was running low on my alloy and mixed in another five pounds of the lead/50-50 mix and may have gotten the amounts off a little that second time I added. Quite a science this boolit casting. BTW-I did make sure I as holding at 30 seconds and flush with the top of the plunger.

[Ohio Rusty]

I noticed the 50/50 WW/Pure lead boolits I cast 3 weeks ago have gotten harder. Even a week ago, the boolits had that 'soapy' feel from the softer lead. You could scratch the bottom of the boolits easily with your fingernail. Last night they felt harder. They aren't as easy to scratch the bottom now and they don't have that pure lead feel. I think they are ready to start being stuffed into shells and send down range in a blaze of glory !!
Ohio Rusty ><>

[watkibe]

It's hard to believe, but the crystal structure of some metals can change at room temperature over time. They have a room temperature recrystallization temperature. If you don't water drop the boolits, they cool slowly, so the crystal grains have more time to grow, and you get a softer boolit. If you water drop (read "quench") the boolits, they very quickly cool to below the recrystallization temperature. This doesn't give the grains much time to grow large, they just all form real fast when they are still small. This makes them harder.
I don't know if water dropped boolits would also show age hardening eventually...