Mold Cavity size query

[Mozz]

I am looking at making my first mold, fairly basic truncated cone with no lube rings.

If i was sizing it down to .358 what size should the mold cavity be? I will be using 3/97% antonym to lead- so fairly soft.

Regards

Mozz

[NC_JEFF]

I think I would try a mold no more than .001 larger than needed. With a soft alloy I would not expect it to shrink much after cooling. Being a truncated cone without lube rings makes it much simpler to size up if it does drop boolits to small. What are you using them in, 38, 357? Are they intended as light target loads or steel plate killers? With no lube grooves will you be powder coating, hi-teking or lubing with LLA?

JD

[Mozz]

They will be used in target loads with Hi-Tek coating.

Mozz

[Tom Myers]

I am looking at making my first mold, fairly basic truncated cone with no lube rings.

If i was sizing it down to .358 what size should the mold cavity be? I will be using 3/97% antonym to lead- so fairly soft.

Regards

Mozz

This may be answering more than you asked but it will give you an idea of the variables involved in determining suitable mold cavity dimensions for various mold alloys, bullet alloys and casting temperature variations

I realize that your design is simple compared to the various diameters and features on this design. However the calculated diameters and lengths can be compared for a better understanding of the process.

The Precision Bullet Design Advanced (http://tmtpages.com/#advanced) contains the Mold Cavity dimension calculator used to calculate the various dimensions.

You are going to size to 0.3580 so probably your bullet should drop with an as cast diameter of 0.359

http://www.tmtpages.com/LinkSkyImages/forum_images/Mold%20Expansion/A_Test_Bullet_358009_263_gr_Sketch.Jpg


Now, Selecting and mold alloy of Aluminum and your custom bullet alloy of 3% Ant, 97% Lead with a mold casting temperature of 400 degrees, the software calculates the mold cavity dimension to be 0.3605

http://www.tmtpages.com/LinkSkyImages/forum_images/Mold%20Expansion/A_Test_Bullet_358009_AL_CavCalc.Jpg

And, after using the Ogive calculator to maintain the 0.700" ogive radius, the software renders the Aluminum Mold cavity sketch.

http://www.tmtpages.com/LinkSkyImages/forum_images/Mold%20Expansion/A_Test_Bullet_358009_AL_Cav._264_gr_Sketch.Jpg


Selecting a Cast Iron mold cavity with the same alloy and casting temperature results in these calculations

http://www.tmtpages.com/LinkSkyImages/forum_images/Mold%20Expansion/A_Test_Bullet_358009_IRON_CavCalc.Jpg


And, after applying the Ogive calculator to maintain the 0.700 ogive radius the Cast Iron mold cavity sketch is rendered with the resulting radial and length dimension calculations.

http://www.tmtpages.com/LinkSkyImages/forum_images/Mold%20Expansion/A_Test_Bullet_358009_Iron_Cav._264_gr_Sketch.Jpg

Please bear in mind that the calculations rely on known alloy expansion and contraction values and individual alloy selections may not calculate perfectly accurate dimension values. However once an experimental casting session provides real world values, the expansion and contraction factors can be edited in order to return quite accurate dimensions.

I might add that, so far, the initial calculations have been quite close to real world values.

Hope this helps.

[Mozz]

Tom

Indeed, you have replied in much more detail than expected, however you have answered questions that I would have needed to come back to the forum for answers- thank you

Once completed I will follow up with a few pictures.

Regards

Mozz



Dave