Well, sorta. One time a long time ago in another place I cleaned out my .22 bullet trap and threw it in my lead pot full of 20 - 1. I could not cast a shootable bullet. The bullets fell to pieces as they came out of the mold. Bad, very bad voodo. Bad MoJo in my lead pot. Had to throw it away and wire wheeled my pot clean. Thought it would have been pure lead. 

           Joe.

Lead antimony alloys age harden, and then soften. This is published and well known. Bullet alloys never fully cool, and at room temp are still continuously in transition. 
Antimony is moving about the alloy. Hence aging for 2 -10 days to achieve peak bhn, then a slow decay to a nominal bhn.

As for duration in the hot pot, excessive time simply lets fluxing and oxidation chats the alloy component values so tin oxidizes off and usually antimony is lost each flux. So the alloy from bullet one to 200 would achieve differing final bhn if all other conditions are equal, unless you can pour all 200 bullets at once.

This is all well documented, and I'm offering information from some intense research for my metallurgy final in school. 

I think that addressed the basic question directly and didn't tangent or at least I hope it did. 


There was mention of why it would matter if bullet 1 vs 200 had varying bhn.

If one casts a large number of bullets for a variety of service, if the alloy composition drifts over a long casting session, under higher pressure service one may find significant performance variation (read: leading). So bullet one may tolerate 30kpsi and bullet 200 may tolerate only 20 or vice versa depending on alloy component loss.

My experience has been that a lee 10 lb pot usually gets cast fast enough over one load to have the bullets be virtually identical. It's the reload of the pot, wait for temp to come up, wife needs help and walk away, stubborn mold that isn't producing quality bullets consistently so most are going back into the pot,,,,,,,,, that's when there has been a wide variation in outcome.

That's my experience and understanding as I was instructed (read: $.02)

I knew that question would be asked next!

My "experience" has been during water quenching for high bhn magnum handgun bullets and HV rifle. Final aged bhn differential ( and this is not accurate due to " did I quench early or late on that drop??) has been upwards of 10 points.

With air cooled alloy I don't have a consistent enough nor precise enough detection system (lee hardness tester) to resolve the difference where I could put hard numbers to a chart------ but over gotten a consistent 2 bhn change. Again, I can't say that is an absolute accurate number as the lee system uses the pencil shaped microscope to measure and it can be difficult to read with certainty. But a trend develops and 2 bhn is consistent with the trend.

Air cooled alloys just don't swing very far to worry. I've never seen the difference is 28 bhn vs 30, or 8 vs 10.  In shooting that is. Now 8 vs 18, that's notable and there will be significant performance changes detected.

On the contrary heat treated and direct quenched bulleta swing violently across the hardness scale and that is where the resolution of change is magnified and easily detected in shooting.


All for the sake of discussion as I expect most all assra shooters are using air cooled alloys ( maybe I've gone to far but it is SS rifle and those are rarely in need of high strength bullets- bpcr certainly doesn't have a place for them). I don't think many here are shooting 50kpsi cartridges with cast, but I've been very wrong before. I don't see the 30-06 and 308 being discussed here, usually some 32 or 25 cal smokeless
Or 38-50 cal BP.

I believe the topic is moot except for all but the most sensitive rifles/cartridge/purpose.
If you shoot. 30:1 bullet and it drops to 25:1 in alloy, which would slightly alter the alloy bhn, is your rifle going to display that change tangibly? I doubt it. I suppose you might see poorer fill out in the bullet, a dimensional difference by a few tenthousandths, but that's it!!! And really that's all that can happen, unless this becomes the ASSMHA ( single shot magnum handgun assoc). 

Am missing any potential options or criteria?

Lots of words to attempt to say eloquently- it won't matter practically- for 95 percent of the shooters on earth. Relative hardness is relative and for SS low velocity or bpcr, minutiae that can be ignored, except that a basic nominal value should be derived for the application and for the sake of consistency try not to have it change too far.

corerftech,
Can you cite the sources that say "tin oxidizes off and usually antimony is lost each flux."

Thank you,

Frank

frnkeore wrote on Dec 21^st, 2015 at 2:54am:


The effects are minimal for each casting session.

  But if you look at the add-metal alloy used to restore the tin and antimony to Linotype there is the evidence that the effect is real needs to be addressed. This might have to be done every month or so under heavy use.

Refer to the print industry reference material and historical loss of alloy components during Linotype reconstitution. 

Have you ever seen a blue or other color skim on your alloy?
Would you like to argue that this skim is not an oxide of one of the three components?
Anybody like to argue that of the three components most used in bullet alloy that tin has the lowest vaporization temp and thusly the lowest oxidation temp and highest oxidation rate?

Oxides being fluxed back into an alloy fully is bs.

Wax and wood chips won't do that. If you skim your melt, your losing alloy components in order of temperature. Rather than argue what is clearly accepted in the industry and is physically unavoidable ( loss of metal during smelting due to oxidation), I'd rather be debating other topics. The ratio of loss over the three components can't be determined. Antimony is suspended in tin and lead therefore antimony goes away in some quantity each time you skim as the tin oxide is generated. Antimony is the single largest contributor to hardness increase due to its precipitation during phase change. If you need a primer happy to post a link to a very good one. 

It's a solution, not an ionic or covalent bond. It's salt and pepper except liquid. You have to quit thinking thinking that if you burn the pepper corns that you can unburn them by adding wood and wax! They are still burnt, oxides might be in solid solution suspended but that it. 
This isn't water and vinegar, it's water and oil in Italian dressing. Only mixed up when you shake it and it's only there when conditions are correct. And even then that's not a perfect parallel to draw, and I'm Italian!

Bullet weight is not measurable with the accuracy needed and bullets are not formed with the accuracy needed to be able to compare weights effectively. If you cant discern the fleck of carbon inclusion weight  in diamonds that must be seen under microscope, then your not going to measure weight changes in the bullets due to minor alloy loss. It takes radical alloy shifts to produce measure able density changes!

But crystal structure WIlL change due to alloy loss and that's what generates the bhn increase or decrease. You can't track weight vs bhn! There is no relationship. 

The discussion was bullet hardness, not hardness to weight relationship To which there is none.

I'm trying hard to stay precisely on topic. Bullet 1 vs bullet 200, bhn difference, does it matter.

Um, "unburning the peppercorns" is exactly what fluxing does.  Scavenges the oxygen from the tin oxide, and allows the pure metal to return to the solution.  Of course, if you skim before you flux, this can't happen, and you lose it.  

Agree that our hardness testers are too crude to measure the difference - at least mine are, and I've got three different ones.

The old timers may well have been fooling themselves, but then again maybe not.  Can we ever know?

  Here are some of my observations, which in my opinion are worth as much as anybodys.
  I cast a 217.2g spitzer B&D bullet from 25-1 alloy at 850F. I flux with beeswax before I start and then from time to time (maybe 10-15 bullets) I skim the dross with the dipper (without fluxing) and knock it into a cast iron pot. Obviously I'm skimming off a lot of tin (according to some). Other than a few light ones in the beginning while the mould gets up to temperature, the rest weigh within .1g from start to finish. Now, after some number of casting sessions the pot of dross gets too full for effective knocking of the dipper so I melt it up, flux, skim well and get 5-7# of "alloy". I saved this skimmed alloy until I had enough for a 20# potfull and then cast a batch of bullets from it. "Lo and Behold" they weigh exactly the same as the ones from the virgin alloy! How can that be if I was skimming off a high percentage of tin?!
  Now before somebody says the change in the tin content was too small to measure by weight; these bullets in 25-1 weigh 217.2g and in 30-1 weigh 219g.
  Yes, I shoot my bullets in the order cast, but that's just pure superstition.