quote [OK, I know between 0 and 1% about casting, but I read somewhere that hardness from water dropping actually fades over time? Is that true?/quote].
Ole Smale is on the money on mixing, but I can't resist interjecting my experiences with casting, mixing and shooting the end product (Bullets).
Since 1/1/2002 I have cast and shot 19,414 bullets in rifles and Thompson single shot handguns. The database goes back to 1996 with over 45,000 rounds recorded. A lot of the entire count was with handguns for Handgun Silhouette type of shooting.
A large quantity of the bullets were cast with 2% tin and wheelweights. I chronographed 25-06 cast bullets at 2245 fps. No leading and great accuracy out to 421 yards (Rifle Silhouette Range out to 500 Meters). I also, run 173 grain bullets from a 26" barrel 308 Win at 2054 fps very accurately. All others are slower.
To meter the amount of tin added, I used pure tin and cast a 200 grain 357 mould with it. Then, I weighed several bullets to come up with a weight that would be 2% of a given weight of wheelweights. The 200 grain mould cavity produces a very light weight "Tin" bullet.
Many years ago, I came across a source of linotype and then to simplify my mixing, I pour all of my metal into 1 pound ingots. Then I mix 3 pounds of Wheelweights with 1 pound of Linotype. I have a Saeco Hardness tester. This mixture comes out at 7 on the scale of zero to 10. I have no barrel leading at all.
If your bullets are harder than 7, they will most likely lead the barrel and cylinders. The bullets will not be as accurate in my experience. However, I have a friend that has had great accuracy with pure linotype bullet s in a custom rifle.
If you shoot steel targets, the softer the lead the better. Hard bullets shatter and lose the momentum needed to topple a target.
I have been retired for a long time with the time and I designed a shooting/reloading database. I keep records in my database of my cast bullets that I have loaded and shot. I keep all loading records whether cast or jacketed.
I have tested water dropping and oven heating to temper the hardness of bullets. I don't do that after running tests.
Bullets with my mixtures continue to become harder from one day after casting and cooling. I have dated and set aside bullets after recording the hardness on the Saeco Tester of 7. I retested the bullets after 2 weeks, 3 weeks and 4 weeks up to 6 weeks. At 6 weeks the bullets reach a maximum hardness of 7.5. The amount of softening that ocurrs from that time is so minimal that I cannot measure it. I had way too much time on my hands, don't you think?
My mixing policy is "If it will melt, I will cast and shoot it, within reason". I have such a great time with cast bullets and phenominal accuracy that my shooting crowd declare that I have made a pact with the Devil.
The reality is that take your casting seriously for safety purposes and don't sweat the mixes, water dropping and oven melting. Wups, as I was writing that line, the memory of borderline melting some oven baking cast bullets went through my mind. My Wife was a bit upset. My bullets didn't melt, they just slumped. I keep all bullets cast on a give session separate and date the cast date. That way, I have a consistent mix for that group of bullets. I try to cast 500 to 1000 bullets in a day. I use four 4 cavity moulds at a time and run them one after the other and start on #1 again.
If a bullet is only surface hardened when water dropped and it is later sized down a thousandth or so, it loses all the benefit from the hardness gain.
One thing to remember about sizing is to fill the intended lube rings full. The bullet obturates when it enters the barrel. If part of a lube ring is filled, the part that is not filled will try to obturate. Therefore, accuracy from an odd shaped bullet will wane.
I have the results of a test done by a fellow about bullet hardness, obturating and accuracy. The Article was published in the Cast Bullet Association monthly years ago. The bullets were recovered and photographed. I have scanned this info and it is on a DVD. It is too large to share on the Internet.
Harold Clark