View Single Post
Old April 13, 2013, 01:07 PM   #9
Join Date: March 4, 2005
Location: Ohio
Posts: 13,648
I used to work for a company that made pyrometers, but they were a low mass black target with a temperature sensor in a housing with a fused quarts window. Infra-red radiation passing through the fused quartz heated the black target. In that way it measured temperature increase in the target due to the IR radiation, and the temperature being measured was derived from that and was read directly on a scale. Pretty much a precursor to today's modern IR thermometers. So I'm thinking the heated element you describe was controlled to a particular temperature by means of feedback from a pyrometer.

At any rate, that heated element would clear up the whole problem with visual temperature judgment, which is variable ambient light conditions. The reason some low number Springfield '03 receivers suffered burn embrittlement was the heat treating oven temperatures were judged visually without such a reference. Despite the workers being experienced, when they got a pyrometer in place to check temperatures, they found the visual judgment was missing by up to 300°F or so just depending on whether it was a sunny or overcast day or if it was early or late in the day, because of how the difference in ambient light affects visual perception.

Those who own a lead melting furnace that's temperature-controlled could set it to 725°-750° and then turn the lights out to get a visible temperature color reference. Indeed, that's probably a good thing for them to do at least once so they can appreciate just how dull the red should be. Once you go beyond that you are growing the metal grain structure and losing more tensile strength.

The methods recommended by Fred Barker in a 1996 article in Precision Shooting as safe, which he describes in one long sentence in all caps {I've not used the caps here}, is:
"(1) Lead Pot Method: heat lead to 725°-750°F; dip neck into powdered graphite and then—holding body of case in fingertips—into molten lead: when case body becomes too hot to hold slap case into wet towel; or

(2) Candle-flame method: Hold case body in fingertips, place case neck in flame and twirl case back & forth until case body is too hot to hold, then slap case into wet towel; wipe soot off neck % shoulder with dry paper towel or 0000 steel wool."
Apparently the candle flame has a very hard time causing the brass to overheat, whereas the faster sources of heat (i.e., torches) can supply heat fast enough to overheat or even melt the brass if you don't use a temperature indicator. One sign of overheating is when the oxide stain formed on the neck is dull looking. A number of people have learned to anneal by polishing the brass first, then just watching for the oxide color to be right. I am leery of that approach because of the ambient light condition variable. They would need some kind of reference again.
Gunsite Orange Hat Family Member
CMP Certified GSM Master Instructor
NRA Certified Rifle Instructor
NRA Benefactor Member
Unclenick is offline  
Page generated in 0.10933 seconds with 7 queries