Lee 6 Cavity Bullet weight observation

[BJung]

I made an interesting observation today of bullets I cast using my Lee 6 cavity 9-120TC mold. I cast a good number of bullets last week and separated them by weight: 124gr, 126gr, 128gr, and 131gr. I decided today add bullets I had cast last year from the same mold, using range lead from the same source. I weighed these bullets and they grouped: 124gr, 126gr, 128gr, and 131gr. The ratio of the two batches were the same. Some 124gr and 131gr bullets. Most of the bullets weighed 128gr and almost as many 126gr. Can it be that the cavities are slightly different?

[M-Tecs]

Can it be that the cavities are slightly different?

Yes....

[Winger Ed.]

It isn't just with Lee molds.
Some of the folks that are seeking the best group, and want to eliminate the last
little variable will use boolits from only one cavity even on Iron molds.

Here's one for ya:
Cast a handful of boolits from one cavity on your Lee (or any other) You'll probably see
small differences in those too.
I never tried it, but have heard you can weigh out jacketed ones, and find little differences in them too.

It might be my imagination,
but I think frequent and aggressive stirring of the pot helps minimizes that to a degree.

If the weight difference is only one or two percent---
Not too many people can shoot well enough that it would be noticeable.
Especially without putting them through some high dollar, tricked out shooting machine.

[charlie b]

For the accuracy I want with the rifle I weight sort to 0.1gn. Yes, there can be a weight difference. Not always.

Before I did that I weight checked some 168gn Amax, 168 Sierra Match Kings and some 155gn Bergers. The 168AMax varied by a bit less than 1gn. Surprised me since they shoot pretty good. The SMK's were 168gn +/-0.1gn (167.9 to 168.1gn). The Bergers were almost all spot on, but a few came out 0.1gn off.

Does it make a difference? A little bit. The jacketed bullets I can tell the difference in group size of the AMax vs the other two, especially out at 600yd or more. 1MOA vs 0.5MOA. For the cast bullets I find a wider range of weights (0.5gn spread) gives me groups over 1.5MOA while the 0.1gn sorted bullets group closer to 1MOA.

OTOH, I don't bother to weigh pistol bullets. Cast, size, shoot. I rarely shoot more than 25yd with them.

[Larry Gibson]

I have 16 Lee 6 cavity moulds. Once I learned to not hold the sprue plate handle and to back it off slightly which keeps the blocks from canting open slightly, to keep the mould warm with proper casting tempo, to keep the alloy temp at 715 - 725 degrees and to ensure the sprue plate was flush with the top of the block the weight varience to any degree went away.

The biggest problem is the sprue plate on the Lee 6 cavity moulds can bow slight up causing the middle 3 +/- bullets to weigh slightly more. Keeping it flush with the top surface of the mould block is essential to uniform weight of bullets. Of my 16 Lee 6 cavity moulds on 4 of them I have removed the sprue plate from the blocks, removed the handle and then with a course piece of emery cloth on a level hard surface have sand the bottom of the plate until it sits flush on the blocks.

[Screwbolts]

What Larry says, technique, timing, observations of results for needed modification are so important.

[Dusty Bannister]

I have several Lee 6 cavity molds and the slight weight variation is not high on my list of concerns. I use a volume powder measure and suspect that the weight of the dropped charge will have more affect on performance.

The bullet as cast diameter is more of concern to me. I have one mold for the 45 cal that really needs to have the cavities lapped to be uniform. Variance from .451" to .453" so must have been a Monday or Friday production. This is where "size really matters".

[fredj338]

If you are worried about pistol bullet wts, you are over thinking it imo. Rifle, sure, weigh then, but even 1/2gr diff isnt affecting accuracy much, even out to 300y. As noted, your case volume may vary that much.

[Ia.redneck]

I have noticed the same thing as Larry with the 6 cav Lee's. That long sprue plate will bow in the middle.
Opening the notch where it contacts the stop pin seems to help that some. Like the plate expands and has nowhere to go but up.

[charlie b]

If you are worried about pistol bullet wts, you are over thinking it imo. Rifle, sure, weigh then, but even 1/2gr diff isnt affecting accuracy much, even out to 300y. As noted, your case volume may vary that much.

Agree, especially pistols.

Rifles still not much. 3-4" (0.1gn) vs 6+" (0.5gn) groups at 300yd, at least with my 210gn .308 bullets.