Temperature DOES Effect Bullet Weight ...

[John Boy]

Keep the temperature of your melt within a 5 degree variance because temperature differences does create variances with the weight of your bullets!

Example:
Melt Bhn 9.8 ... 20:1 is Bhn 10.1
Ten Pounds of Melt in a 20# Cast Pot
Bullet Mold: PJ 45001 Creedmoor, nominal weight 540gr
100 Bullets

660F - 542-542.9gr - 8 Bullets = 8% ... Mold was not hot enough
670F - 543-534.9gr - 49 Bullets = 49% ... The correct temperature, bullets dropping nicely
680F - 544-544.9gr - 31 Bullets = 31% ... Thermometer tilted and I didn't notice it
690F - 545-545.6gr - 12 Bullets = 12% ... Thermometer tilted and I didn't notice it

And ...
At 670F, the sprue puddle was frosting in 5 seconds - Perfect! All bullets at 543 to 543.8gr variance
At 680 - 690F, the sprue puddle was frosting in 7 - 10 seconds - Mold too hot!

So, regardless of the mold, hold your melt temperature within a 5 degree variance so the sprue puddle frosts in 5 seconds. You'll then have good looking bullets and a small weight variance

And on bi-metal thermometers, there is a band on the stem. Make sure the band is ALWAYS in the melt! Otherwise - incorrect temperature readings, usually a lower reading

[bobk]

Ah, John, that's pretty uniform, regardless. Much less than 1%. I'd bet even your rejects would shoot pretty good, for someone of my skill level. :wink:

Bob K

[randyrat]

Not to argue, but i find a difference when my mold is not up to temp also. All my molds work better when they are up to stuff/temp.
I find sticking, inconsistant weight/size with a cold mold. Of course, alloy's have a lot to do with it also.
I find it absolutly neccessary to keep my mold up to temp if i want consistant boolits ( Not to under estamate the importance of the melt temp). I like my boolits just glazed/frosty slightly, then i know i got the temp of the mold and the melt perfect. I've never owned a thermometer.
You have a lot more gumf/patients in you than me to measure all those temps and weights. Good job