I have weld away numerous of stocklugs and lanyardrings slots etc.
It's fairly simple.
Get a welding vire that fits the luger steel well, some kind of carbon vire, absolutetly not any modern tool steel vire.
Preheat the frame to 200 celcius.
Weld it in small portions, let it cool down in the furnace between each welding till the 200 celcius.
Betwen each weldign clean all surfaces very carefully and don't forget to have totally clean and degreased weldingrod.
When finnished with the welding let the frame cool down to normal temperature in the furnace so the temperature goes down as slow as possible.
After the gun has been welded its likely that the weld still is harder than the rest of the gun and one way of getting that hardness down is to heat it with a torch at the place of the welding. THis avoids strange colorations.
DON'T temper it higher than 200 Celcius in the furnace as the hardening on the camcurve then will be lost.
My .02 cents......
Regards HÃ?Â¥kan
ps. I have this way welded at nearly 100 cracked SIG P210 frames.
http://www.vapensmedjan.com