Butt splice connector to join 10 gauge to 12 gauge wire?

Looks like they lost or tossed my last note so I'll try again. After 55 years as an electrician, making thousands of joints from 12 volts to 13,800 volts I can say I never soldered a joint or termination. I am reasonably sure all those plants, commercial buildings and homes are still there and likely have had zero issues in my joints and terms.