After reading the "how do they make steel wool" thread above has got
me wondering..

How do they make copper "solder ring" fittings?

I can see that the actual copper part could be bashed out by a big
machine but how do they get the solder into the groove on either end?

You could sit there for days trying to get the solder into the groove
with a blowlamp/soldering iron and never achieve it.

The joints don't appear to have any discolouring due to heat.

So..how do they do it?

sponix