Strange phenomenon when sizing

[Humbo]

I was sizing bullets the other day, and experienced something strange. I bought a couple of LBT molds earlier, one 340 gr .452 WFN and the other a 300 gr .452 LFN. Both dropped bullets right at .453, which is good for .452 sizing. The LFN was right at .452 after sizing, but the WFN was .4515. Why the difference? Alloy is the same, molds are from the same manufacturer, casting technique is the same, sizing die is the same, as far as I can tell all conditions are the same, except the bullet designs/weights. Very strange.
I will try to cast with both molds at the same time, with exactly the same outside and pot temperatures and then see if the results are the same. What else can cause a difference like that?

[andremajic]

I'm thinking that maybe there is a hardness difference between the heavy bullet compared to the lighter one, even though you're using the same alloy. Thermal mass from having more molten metal in one over the other may affect how fast it hardens.

Or, If you are sizing a softer bullet, it may "swage" into the sizing die better when force is applied to the top of it, squeezing it to fill the die better than the harder metal. Maybe the lighter bullet is softer?

Do you have a proper fitting punch that is the same shape as the ogive?

Your lighter bullets may be harder than the heavier ones. If they are harder, maybe the die is "shearing off" more precise amounts of lead off the sides than the softer bullet, with more "tearing" off the edges of the softer metal on the larger bullet.

I'm almost convinced that it has to do with bullet hardness.

I have made some dedicated sizing dies for specific bullets by grinding some extra metal from the sizing punch and using release agent on the bullet, put some fill the ground out area with epoxy and insert the bullet tip into it. Use qtips and vinegar to clean up any excess epoxy that oozes around to clean it up. When the epoxy cures, remove the bullet and you have a dandy little sizing punch that is custom made for your bullet, which will help prevent your bullets from deforming.

Just a couple ideas. I might not be right, but I had to try and figure it out. Let us know what fixes it.

Andy.

[Humbo]

Andy, thanks for your reply. Actually, it is the heavier bullet that is smaller. I'm using a Star sizer also, sizing bullets nose first so no need for extra bullet punches. But it might have something to do with bullet hardness, I'll measure both bullets and see if there's a difference. I think I found the heavier bullet a little easier to size also.

[243winxb]

Bullets are not perfectly round as cast. There can be as much as .002" difference on just one bullet. After you size, the lead springs back. The high spots that were sized more, will measure larger than other. You need to measure your cast bullet as they can not be perfect .453" in all areas. Or after sized a perfect .452" Just my guess, better measurments are needed to .0001" not .001":smile:

[BD]

I don't know the answer to your question, but I'd sure like to try some of each of those designs in the .450 bushmaster :) There's not that many molds out there at 300 grains and up that drop .453.
BD

[kywoodwrkr]

Were the two boolit types cast at the same time?
In other words is there a fairly large time frame between their birth?
Boolit hardening due to time since cast may be a factor.

[Humbo]

BD, I'd be happy to send you some, but I think postage from Norway is a bit steep.

kywoodwrk, the lighter (also larger in diameter) bullets had a couple of more days to harden, so I will try to cast some at the same time and see if the difference is still there.

[Larry Gibson]

Humbo

You answer your own question; "Why the difference? Alloy is the same, molds are from the same manufacturer, casting technique is the same, sizing die is the same, as far as I can tell all conditions are the same, except the bullet designs/weights."

The different design allows for different "spring back of the alloy after sizing. One can cast numerous different designs of a caliber just as you did and have slightly different sizes after sizing just as you did. Nothing new or strange there at all, happens all the time.

Larry Gibson

[lathesmith]

This is yet another reason to keep around more than one size of sizer for a given caliber. I used to think Lyman recommended this just to sell more dies, but with posts like this and other occurances I realized the wisdom of their advice.
lathesmith