An interesting simple casting experiment

[TexasMac]

I knew that the alloy temperature affected bullet weight but had never determined how much. Normally I went with the temp that resulted in fully filled out bullets using a specific alloy. Since I planned to cast sufficient bullets for 3 silhouette matches I figured I’d run a simple experiment. So I just finished casting & weighing 3 batches (60 bullets/batch) of .40cal 400gr bullets using the BACO 409400M5 (old 409400M4) mould and the RCBS Easy Melt PID controlled furnace.

The 1st batch was cast at 765 degrees & weighed 400.0grs +/- 0.6grs. The alloy temp. was increased to 770 degrees for the 2nd batch which weighed 401.0grs +/- 0.3grs. So then I lowered the alloy temp. back to 765 degrees for the 3rd batch with dropped back down to the same weight as the 1st batch (in this case the weight was 400.0grs +/- 0.5grs). So now I know that 5 degrees will result in a change of approximately 1gr.

BTW, the alloy was verified as 15.7:1 by measuring the specific gravity using a laboratory grade high precision scale.

Wayne

[John Boy]

So now I know that 5 degrees will result in a change of approximately 1gr.

Wayne - good information, Thanks for the post

[GrumpyBear1]

So if your lead pot's rheostat isn't controlling precisely that could be a reason for a significant weight spread when casting with a known alloy. Oh and I was using the same mold as you. My bullets are coming out in the 394-396 range with 16:1.

Very interesting Wayne, Thanks.

[John Boy]

Wayne, I have never casted over 730 degrees but at this temperature never had an issue with quality of bullets and weight variance.
Next session, I'm gonna kick the temperature up to 770 and see what happens. Next session is 535gr PJ Money bullets for rounds needed to fill out a 100 round box
Regards
John

[Bakebfr480]

How is this possible? Inquiring minds want to know!

[rjmelehan]

How is this possible? Inquiring minds want to know!

Anyone....? Ferris....?
Very small voids perhaps...?

Forensic review of my lighter than usual bullets
usually revealed a void..

bob

[TexasMac]

How is this possible? Inquiring minds want to know!

Anyone....? Ferris....?
Very small voids perhaps...?
Forensic review of my lighter than usual bullets
usually revealed a void..
bob

It's not a void issue. My best guess is it's the result of the mould expanding due to the increased temperature. I repeated the experiment a little later with similar results. See the thread at the following link: http://www.shilohrifle.com/forums/viewt ... re#p312239

Wayne

[jonp]

Interesting results but I seriously doubt that you can cast enough bullets accurately enough replicating everything close enough to detect a 1gr difference in weights and associate that with temperature only. With a 400gr bullet that is .25% variance in weight which is well under the average variance you get just casting bullets.