weight variance of cast RBs

[Salty]

I cast 495 RBs with 99% pure lead. They are supposed to weigh 182 grns. I throw back anything under 182 assuming a bubble.
I have been using 182-183.9

Is that too much of a variance? Could the heavier ball have impurities that could throw off accuracy?

Of you that weigh your RBs, how much of a variance do you keep?

[Bigsmoke]

Frankly, I think that little of a variance doesn't really matter, especially if you are shooting from an unsupported position.
However, if one is in for very competitive bench rest shooting, I would weigh everything:  the balls, the powder charges, heck, even the patches.
But, what do I know?  Heck, I think by now I have forgotten most everything I ever did know.

[KDubs]

I don't think that variance is bad at all but as bigsmoke says, what do I know.
kevin

[No Powder]

Although I weigh, and try to keep them within + or - 1 1/2 grains, I think what John and Kevin is 100% correct. Human error will eliminate any perfect results you are trying to achieve. Although, if I find any huge differences in weight, those will get recast. [ Invalid Attachment ]

[Salty]

Thanks fellas.

No powder, it looks like you have them grouped to within 1grain.
Have you found any difference in accuracy between the tree groups?

[No Powder]

I cast more 490's with that mold than any other ones. Therefore I have a lot more of those, and that's the reason for only 1 grain weight difference. In the .530's and .440's, I have more fluctuations in their weights. I haven't been able to see any differences shooting the different weights. Sometimes it doesn't matter how simple I try to keep it, I make it harder than it should be.

[RobD]

"Pure lead" is generally unobtainable as all lead will have some manner of contaminants.  This can vary the projectile weight - far less with lighter weight castings in the 100 to 200 grain range and lots more when the cast weights are well over 400 grains.  This is noticeable even with tin:lead alloy cast projectiles.

Improper casting that allows air to remain in the mold is the chief reason for projectile weight variations.  That's typically due to pouring in the lead from above the mold rather than "compression casting" the lead into the mold.

Over the decades I've found that "compression casting" lead or lead/alloy projectiles allows the best cast dimensions and weight.  Getting both the lead and mold up to an operating temperature that both like best will make for better casting.  I heat all molds up separately on a hot plate while waiting for the lead to have well melted.  A few first castings are usually discarded, then the real casting begins, which is a process that should be smooth and easy, with no interruptions. 

I almost always cast two molds at a time - whilst one is cooling a bit the other is getting poured.  Having a timed routine for pouring and extracting is important, with NO interruptions in the casting process.  Having a ladle with a snout is the only way to go for compression casting, where the snout gets into the mold sprue hole @ about 45* and then both are smoothly flipped over level (this is the compression part), the ladle is extracted, and remaining ladle lead is allowed to cover the mold top.  Pouring lead into a mold without having the ladle in contact with the mold will yield the greatest variant in projectile weight and overall uniformity. 

[No Powder]

I totally agree with Rob about the remaining lead in the ladle covering the top of the mold. When I do that, I always seem to have more consistent results.

[RobD]

I think whats important with casting lead or lead alloy projectiles is keeping the heat cooling uniform.  When pouring lead into a mold it's starting to cool during the drop.  This is eliminated by getting the ladle snout into the mold.  It isn't so much about compression as it is with getting hot lead into the mold ASAP.  Dumping the rest of the lead onto the mold top helps for a slower loss of heat.  Whatever the reason, compression casting along with a full ladle dump always works best for me, no matter if I'm casting pure lead balls or alloy slicks and bullets.

[No Powder]

Sometimes when I'm using a bag mold and empty the ladle on it, those strands of lead that overflow will not permit the opening of the mold. So they are simply broken off and threw back in the molten lead. Some of those strands snap right off. Some have to be bent back and forth several times to get them to break off. Is that an indication of the purity of the lead or does it indicate something else?

[RobD]

Sometimes when I'm using a bag mold and empty the ladle on it, those strands of lead that overflow will not permit the opening of the mold. So they are simply broken off and threw back in the molten lead. Some of those strands snap right off. Some have to be bent back and forth several times to get them to break off. Is that an indication of the purity of the lead or does it indicate something else?

I dunno for sure.  "Pure" lead shouldn't be brittle and if it is then I'd think it's not "pure" and is either an alloy and/or has contaminants.  Melting lead or lead alloy (tin and or antimony) all needs to have the dross removed continually, as well as stirred often.

[Salty]

I have been buying my lead from RotoMetals. They claim 99% pure but what do I know. Anyway I expect the balls under 182 have air bubbles. But over 183 I bet there is some sort of impurities. But what is heavier than lead that could be mixed in there?
I?m gonna need to read several times how RobD does a compression casting. Sounds interesting. I now pour from a Lee bottom pour.

[RobD]

After decades of casting with a ladle I tried a Lee bottom pour, thought it would save time and be easier than a ladle ... terrible experience, what a mess, inconsistent weights, gave up and went back to the ladle.

[Salty]

RobD, do you know of a video demonstrating the compression method? I searched on YouTube but couldn?t find anything.

[RobD]

RobD, do you know of a video demonstrating the compression method? I searched on YouTube but couldn?t find anything.

Compression casting .45-70 slicks, 1:16 tin:lead alloy ...