That thought had crossed my mind...! I guess the good thing is that the force on the iron spreads around a large area and the opposite force on the tube is very concentrated.... so the softer copper will always give.
True, but I almost got sick while hammering that lifter down into the bore. If that thing woulda let go-POOF! $1000 up in smoke! Think I’ll have my brother do the next one just so I don’t have to watch!