Too much tin?

[ScottJ]

So I tried out my new Lee TL356-124-2R Saturday.

Unlike the last new Lee I bought it's not undersize. Getting about .358 out of each chamber.

But they're all drastically underweight. 119.6 grain on average.

I'm thinking maybe I have too much tin in them but am not sure because the used 358-140-SWC I bought casts 139.4 on average and I got that out of this same run.

I was hoping to get a true 124gr since I think the RCBS mold I've been using drops about the same (it's supposed to be 115 gr).

[HeavyMetal]

If Lee cut the cavities a tad short that would account for the weight issue.

Since you used the same alloy to cast the RCBS boolit and it's only off by a half a grain or so I'm thinking mold issue.

Will suggest you measure the boolit length, not diameter and post it here with the request that anyone with the same mold post a length measurement to compare with yours.

It wouldn't take much to drop 5 grains from a 9mm mold.

[sagacious]

5grs decrease on a 124gr bullet is not drastically underweight. It's actually pretty close to specs.

You do not specify your alloy, so no one can accurately comment on the question about tin content affecting the cast weight. .358" diam might indicate adequate volume to give 124grs, but with an unknown alloy, all one can do is guess.

Specify your alloy so a correction can be suggested, if possible.

[Ed Gallop]

I get that much variation in the same session but after lube sizing they are more consistent. Ed.

[243winxb]

Forget the weight, diameter is what matters most.

[fredj338]

The tin would account for the lighter wt & larger dia for sure. I agree, cast dia & hardness is more important than wt. My 45/185gr Dev mold is supposed to be 185gr but casts closer to 200gr using a 25-1 or 50/50 ww/lead alloy.

[MtGun44]

5 gr is a minor wt difference, not drastic.

Bill

[303Guy]

5 gr is a minor wt difference, not drastic.OK - so I weight some of mine and I am getting variations of less than .5grs. Not huge numbers measured but out of a batch I got 4 distinct weight groups. These are likely alloy changes. My molds are solid so there is no possibility of mold closure variations.

Another batch gave as much as 1gr variation which is still less than ½%. How close should the weights be for rifle accuracy?

[MtGun44]

Wait a minute. Do he mean 5 gr less than published wt for the mold or 5 gr variation
amongst a batch of boolits? I read it as the first one and we keep getting guys writing in
"Help me, something is really wrong with my 250 gr mold, it casts 255 grain boolits and I
can't find any loading data for 255 gr bullets, only 240 and 270. How come my mold
is totally screwed up? What can I do?"

This kind of variation is way within the normal variation in alloys, if that is what he meant,
which is what I thought he meant. Also, these molds are cut with a single point cutter,
not a cherry, so that can introduce variation - altho it is supposed to be CNC constant.

If you are getting 5 gr variation in a batch of boolits, this might be pretty bad. With mystery
metal ( a personal favorite) you can easily get this much batch to batch variation, but should
be better than this for one batch of metal, depending on boolit wt. For a 500 gr
boolit, 5 gr is only 1%, not too shabby - but can be bettered by a bunch with good technique.
For a 124 gr 9mm, this is 4%, not too great. HOWEVER, my bet is that they would still shoot
fine at reasonable pistol ranges.

[legi0n]

I have the same mold and with pure lead it indeed produced 124gr.
But any other alloy I tried weighed less. The one I settled for still drops 120gr even after enlarging the cavities.