David,
Water dropping or quenching will only work if there is arsenic in the alloy. Since wheel weigh material can vary quite a bit in alloy, a test will have to be made with your specific batch.

I have had some that dropped from the mould and in a few days of air hardening, came to the 12BHN level on their own. That hardness, if they are the right size for your firearm, bore or throat size +.001" to .002" and you will need nothing harder to 1200fps, that is, if you have enough of the right kind of lube on them.

What bullet style/mould number, are you going to be using? What kind of lube are you planning on using? How are you going to size the bullets?

If you want an in depth study of the subject, look here: NRA - IHMSA Handgun, Rifle, Air Pistol Silhouette Shooting. The Excitement Of Reactive Steel Targets At The Los Angeles Silhouette Club I think this will help. Check out the "Intro to casting" online book. There are lots of articles by Glenn Fryxell and they are required reading, in my opinion.


Back to your original question, 30BHN + depending. So, yes, water quenching does in fact change the hardness of your bullets. There are other ways too, some I think are covered in the additional articles by Glenn.

Hope this helps.

p.s. I have driven my cast bullets in 357Mag to 1580fps from a Marlin 1894 rifle with no leading period. Straight wheel weights with White Label's BAC lube.