Heating a bolt action receiver to 1000*F will ruin the heat treat and make an unsafe rifle. 1000*F is glowing red hot.
Wow, an armchair metalurgist here. There are thousands of guns so treated every year. 1000⁰ doesn't even come close to the tempering heat used. I've never had an issue other than sometimes reduced performance in the bore
You don't know what you are talking about.
I see from the link above that they are really heating the part enough to ruin the heat treat. For reference, the correct temperature to draw a spring is about 750*F. A tumbler is drawn to about 450*F. Depending on the exact alloy a 4140 receiver would be drawn to a temperature somewhere in-between those figures. Heating a receiver to 1000*F and cooling it slowly would result in a dead soft state. When fired the locking lugs would set back making it impossible to open the bolt. I would not let them touch my rifle on a dare.
For items that are not heat treated, like pistol slides and frames I see no issue.
