It would be interesting to measure/chart surface temperature. Some of the information about heat treating bullets could lead us to think that a 1 hour soak in a 460F gas oven does not heat the bullet to the ambient temperature of the oven. One tester used both a gas oven and a convection oven at 460F and the convection oven bullets were 7 brinell harder, both were soaked at temp for 1 hour.
How much heat the substrate conducts would be part of the question.
But until the core of the bullet reaches 400F will the surface temperature be 400F in a 400F ambient environment ?? If we are PC aluminum sheet metal .06" thick the substrate will reach 400F much more quickly than if we are PC a 24" aluminum cube ?? Same issue if we are PC a .224" bullet vs a 20mm bullet ??
Drilling a small hole near the OD of a bullet and inserting a small RTD to chart time/temp would be an interesting experiment.
https://www.omega.com/pptst/FINE_DIA...TD_PROBES.html
Those are small enough that one could be inserted near the outer diameter, and one at the center of the bullet.
For those not in the know an RTD is a resister that changes resistance in reaction temperature change. A milliamp electrical current is sent through the RTD and this allows measuring temperature. We use a lot more RTD at work than thermocouples.
They are IMHO way easier to verify when trouble shooting too, the RTD we use typically ohm out at around 110 ohms at room temperature, they also cannot be wired backwards...a thermocouple can be wired backwards.
Of course surface temperature can be measured with IR stuff but the reflectivity of the surface skews the readings, some PC at a given soaked temperature may read differently with IR temperature measurement. Shiny stuff especially is an issue, most IR guns stink at measuring the temperature of molten lead, they will do fine with a less shiny object floating on the surface.