possible zinc contamanation, you tell me!

[tree rat]

500 S&W loaded with trail boss for real light loads, aprox 900 fps, in encore 20 inch barrel, cast in a lee mold.
I wanted to capture a bullet and see if there was any expansion at this velocity, range was 35 yards shot into clay dirt bank. could not locate bullet. so I set up a 7/8 inch plate steel backer thinking the bullet hit and expand and bounce back about a foot, still no go can not find a bullet. so a freind sugested to put the steel plate in the back of a card board box and try again. well I found out what was happening to the bullets--- this was VERY interesting, one shot to the center of the box. inside was the gas check only. but one inch in front of the plate, in a pattern 1/2 inch all the way around the box 90 degree from bullet path the box was shreaded! these bullets are acting like a hand grenade schrapnal when they hit even at low velocity. I beleive it is zinc contamanation , sat one on concreate and hit with a hammer and it just crumbled. I did mold these very hot and frosty.  wanted to try one on a coyote, but my calling skills suck.

[Lloyd Smale]

did they air cool or did you water drop them? What alloy?

[tree rat]

air cooled ww, but there was a bunch of stick ons that were slow to melt, so not thinking about it I turned the heat up and they melted fine with my lee bottom pour 10 lb at #8 on thermostat, I usualy run on #7. do not have a thermometer. that is why I am now thinking zinc.

[45-70.gov]

did  they  cast ok  otherwise??

i  was suspecting zinc  contanimation   as i was having problens  with wrinkles

[tree rat]

yes I was having some problem with wrinkles, that is another reason I turned up the heat and was casting fast. but I figured it was just the weather, I cast outside, and it was about 55 degree and light wind. it is hard to keep a mold hot enough like that.

[Lloyd Smale]

probably got some zinc. stick ons can be zinc too. Its normal though for lead stickons to take a bit more heat to melt too. Pure lead takes more heat. But if you had casting problems and grainy bullets good chance you got some zinc. Anymore its rare to get a batch of ww that doesnt have at least some zinc wws in it.

[Sweetwater]

If it's zinc contaminated, how's the best way to get anything decent to cast? Add something? Higher heat?

I think I might be experiencing the same thing; was blaming the mold for nose wrinkles and poor fill out.

Regards,
Sweetwater

[Lloyd Smale]

try adding about 5-7 percent tin and casting with your pot turned all the way up and fast enough to just keep the mold from smearing. I even keep a wet cloth to touch the spruce plate with to cool it enough not to smear. casting like that you can get good bullets.

[Sweetwater]

Lloyd-
I will definitely give that a try on the next casting session. Thanks!!

Regards,
Sweetwater

[Tn Jim]

I thought zinc melted at a lot higher temp than lead and WW. Am I wrong?

[John Traveler]

True, zinc melts at 787 degrees Fahrenheit, and lead melts at 671 degrees Fahrenheit.  Wheel weight alloys (mostly lead) melts somewhat lower than pure lead.  That is why the initial signs of zinc contamination in a lead melt is a mushy, oatmeal like layer floating on top of the lead.  You can try skimming off and discarding most of it, but once the melt temperature is cranked up, some of it gets into the alloy.

According to the NRA advisor, once a bullet melt is contaminated with molten zinc, you can never get all of it out, and it would be best to discard the melt, clean the pot, and start over.  That has been my experience too.  Once a batch pours poorly in clean, hot molds, if it fails to fill out even after increasing tin content, I pour it out and start over.

[rangerwillie]

Is there any real harm or damage to the mold or your barrel?

[stubshaft]

Some of the stick on weights contain zinc.  The biggest culprit is usually the european weights they are notorious for containing zinc.  The last time I had this problem, the only thing that I could do waas to throw away the melt and sand blast all remaining traces of lead in the pot (I tried just dumping the melt and remelting known good lead.  It turned to slush from the remaining zinc).
Good luck.