Lee 9mm molds, one casts low, one casts high

[mdntranger50]

I have a Lee TL356-124-2R 124gr mold that drops at 120gr and a Lee 356-125-2R 125gr that drops at 130gr. Both with the same alloy and in the same casting session. Someone tried to telling me that's how alloying works. Well I know alloying lead can make it lighter depending on the composition but that doesn't explain why the same exact alloy drops lighter in one mold and heavier in the other. I guess it's just the Lee mold tolerance in manufacturing?

[Ben]

I wouldn't put too much faith in what Lee writes on the outside of their moulds as to weight of the bullet.

[chriskendziora]

I'll bet if you mic the bullets the outer diameter will be different too?

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[Dusty Bannister]

The as cast weight being heavy or light is not nearly as important to bullet performance as matching the bullet weight between cavities and the as cast diameter of each cavity.

[bedbugbilly]

In the last 60 years I've had many mold od different makes that don't drop at the weight they are supposed to - or consistently for that matter. Take the same mold - cast 100 with the same pot of lead and then, when they cool, weigh each one - if they all weigh exactly the same grain weight, you will probably be the first in history to achieve that.

As far as having two different molds that are supposed to cast the same grain weight - many brands of molds will fail that test as well. Different mold cherries for the same boolit design can vary, with use, mold cherries wear and all of those things can make two different molds for the same grain weight drop boolits that are poured from the same pot of lead drop ad different weights.

As an example, I have 4 different Ideal and Lyman molds for the exact same boolit - 575-213 New Style hollow base Minie ball for .58 caliber rifled muskets. A cording to Lyman, this mold is supposed to drop a 505 grain Minie at .575. In years past, I have cast in all 4 of the blocks in the same session using the same pot of soft lead. One of the set of blocks - an old Ideal set, casts a .565 grain 507 t0 510 grain Minie, the same as a set of Lyman blocks that I bought new about 1963/64. One of the other blocks casts a .5755 Minie and the 45h set of blocks drops a .576 Minie.

Measure the boolits from the two different molds with a micrometer and see what they mic out at. As already mentioned, I wouldn't worry too much about what Lee says they are supposed to drop at as far as grain weight. Whats more important is that they drop at a diameter that you can utilize in your bore size, whether you use them as dropped or size them.

I certainly understand the curiosity of your question as it would seem as though same pot of lead - 2 different molds and that much variance sort of makes you scratch your head - but even with other makes of molds it can be that way more often than you'd think.

[JonB_in_Glencoe]

The Lee 2 cavity molds with old style blocks would very quite a bit, batch to batch, due to Lee's manufacturing procedure. Years ago, I posted about the variance I had with four older style Lee 30 cal molds, a couple were much lighter than advertised. In 2013 when Lee upgraded the 2 cavity block design, they started CNC machining them and they became much more consistent.

https://castboolits.gunloads.com/showthread.php?189534-Lee-30-cal-2-cav-molds-not-necessarily-as-advertised

[BC17A]

I guess it's just the Lee mold tolerance in manufacturing?

You guessed it. It's all part of Lee's "precision"(sarcasm). Not only are the weights all over the place, but some of my Lee molds cast boolits that are up to .007" longer than listed.

[justindad]

I have a 10 grain range in two copies of an NOE mold for a .45ACP round nose boolit.

[mdntranger50]

I'll bet if you mic the bullets the outer diameter will be different too?

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They both measure .3575-.358 as cast then after PC they are .359-.360 I resize to .356 for 9mm and .358 for .38spl

[mdntranger50]

Thanks to all for the insight. I figured it was just manufacturing tolerances but I didn't think it would be that much off. I do not have a problem with these molds as far as casting and they both shot accurately. Just curious as to the big range of variance weight between the 2. Thanks

[Dusty Bannister]

Please do not let a negative perception of a problem with the weight as marked on the molds. Break in the molds, shoot the cast bullets and then determine if they are suited to your purposes. The TL molds are fairly complex and you might find better mold fill out as you work with them. Enjoy them and spend less time worrying about a few grains weight difference from the mold as marked.

Edit: I must be slow thinking this morning. The above posted while I was typing.