Boolits get bigger when they come out of mold?

[GrizzLeeBear]

I'm toying with the idea of removing the gas check shank from 2 of the cavities in a 4 cavity Lyman 358156 mold. I use the GC boolit in my 357 Herrett, 35 Rem and 357 GP-100 for "full snort" loads. But I would also like to have the same boolit with a plain base for plinking loads (1100 fps or slower) in these. Having 2 GC and 2 PB boolits in the same mold would work great I think. So I was doing some measuring. The mold cavities at the base (GC shank) measure .339, a bullet cast from this mold with WW + a little tin measures .344 at the base. So, the bullet gets bigger after it drops from the mold? Is this normal, or am I missing something?

[GrizzLeeBear]

Ok, doing some math.

.344 - .339 = .005
.005 / .344 = .015 or 1.5% expansion after bullet drops from mold.

reaming base with 9mm (.3543") reamer to remove GC shank.
.3543 x .015 = .3593
So bullet should drop from mold at about .3593 (perfect!) right?

[PPpastordon]

Maybe should ream to diameter of mould that cast full size boolit? Whatever that might be?
Just someone's 2 cents.
PPpastordon

[andrew375]

What you are missing is that the mould expands as it heats up, therefore the cavity in which the bullet forms is larger than when cold. Also, lead alloys have a different coeffiecient of linear expansion to iron or aluminium.

Also, what are you using to take these measurements with? If it is a calliper, known in industry as a "guessing stick", then you are wasting your time trying to measure to 2 or three thou' precision due to the mechanical limitations of the basic design. This is why there is no facility for adjusting calibration like there is on a micrometer.

[Duckiller]

You missed the section on size vs alloy in your Lyman Cast bullet Manual. Pure lead cast smallest. As alloy gets harder the boolits get larger.

[leftiye]

I agree with Ppastordon, Measure the lands (grooves in mold) of the mold (maximum diameter of mold). Then get a drill or reamer that size. Put the drill or reamer (flute end) in a smooth jawed vise, and make sure that the (inside) measurement of the vise jaws is the same as the measurement of the inside of the mold was. Make sure you use the same inside calipers you used on the mold! This will take out any miscalibration problems.

[GrizzLeeBear]

Thanks for the input guys. Yeah, I guess the easy way would be to measure the "fattest" band in the mold and ream the base out that size. Duckiller, I did re-read that section of the Lyman book. It does shows how one alloy relates to another, but not how the actual size of the mold cavity relates to the size of the dropped bullet.
Anyway, the more I think about it, I think I'm going get a Lee 158-rfn 6 banger to make PB bullets and leave this mold alone for now and maybe have one of the cavities made into a HP. Then I would drop 3 regular GC bulllets and 1 HP at a time. I think a 358156 HP going about 1800 - 2000 fps would make a fun woodchuck load out of my Marlin 35 Rem. ;-0