I have rather some experience with isotope lead. I have a source that works at a hospital. I am able to purchase about 1,000 lbs /month. The lead ranges from small vial containers all the way up to the 30# reactor cores. Some vials are painted, and some are not.
For my son's recent science fair project, we undertook to test the effects of various hardening techniques on the lead. Let me summarize our findings.
We cast 180 samples each at 650°, 700° and 750° as indicated by a lyman themometer from a Lee Production 4 10# pot. The samples were 175 gr SWC TL from a Lee six-cavity mold. At each temp half the samples were air-cooled, and half were water dropped. No bullets were retained during the mold 'pre-heat' period of casting.
The ingots that were replaced in the pot were all made from a single smelting session, from the same component lead. The lead ingots averaged 13.33 BHN on a Lee Tester. Lead was added to the pot after each 180 bullets, along with any accumulated sprue's. The ingots were sorted as to ensure average hardness lead was added each time. The number of each ingot and the sequence it was added was recorded for use in more advanced analysis later (if I have it in me).
Once cast, bullets were divided into 18 groups of 10 bullets. These groups were a control of the air-cooled and quenched at each temp (total of 6 groups), 6 groups that would be annealed for 1 hour in a 350° oven, then air-cooled, and 6 groups that would be heat treated for an hour in a 450° oven and then quenched.
Group 1-6
Cast Temp 650°
1,3,4 air cooled to an avg BHN of 10.53.
2,5,6 quenched to an avg BHN of 25.88
3,5 were annealed to an avg BHN of 10.83 and 10.67 respectively
4,6 were heat treated to an avg BHN of 16.44 and 17.38 respectively
Group 7-12
Cast Temp 700°
7,9,10 air cooled to an avg BHN of 11.23
8,11,12 quenched to an avg BHN of 29.50
9,11 were annealed to an avg BHN of 9.72 and 10.13 respectively
10,12 were heat treated to an avg BHN of 20.46 and 21.83 respectively
Group 13-18
Cast Temp: 750°
13,15,16 air cooled to an avg BHN of 11.77
14,17,18 quenched to an avg BHN of 32.41
15,17 were annealed to an avg BHN of 9.86 and 10.37 respectively
16,18 were heat treated to an avg BHN of 24.87 and 25.33 respectively
The average weight of the samples ranged from a low of 172.08 (Groups 1,4) to a high of 173.66 (group 18).
I have retained the samples, and intend to test them again for age-hardening and final diameter and length.
Hope this helps.
involved pushing my truck key into them, and then a wheel weight...then the sinker again LOL!!! I really need to pick up one of those Lee lead hardness testers. 
