We have a wide range of tubular and honeycomb cores available. All of these cores are made from individual tubes, soldered together to produce the two types of vintage radiator core in popular use. All cores are manufactured using 70/30 brass tube, dipped in 50/50 tin/lead solder, to their front...
Not in any way helpful - but many years ago, one of my earliest design jobs was a large semi-automated rig to pressure test cores straight after manufacture for one of the big names in core manufacture who was local to us - still there and still going strong - a rather large engineering manufacturing copany that unless you know, you would drive straight past and continue to think there was no engineering around there . . .
I assume the several machines we made are still there and still operating.