Question: Every so often while shortwave listening I’ll come across a frequency where tons of hams are talking all over each other giving a call sign and a six digit number only (not a QSO). I imagine these numbers may be club membership numbers but I can’t figure out the purpose. Is this some way to build up a large number of QSOs? Doesn’t seem like the requirements of a QSO are met by just getting a call sign and number. And how on earth does anyone copy all of these contacts given that everyone is pretty much talking over themselves, voices overlapping, with no moderator or any attempt to direct traffic?

What makes this even weirder is that I’ll sometimes hear other hams on the band who mention this but don’t know what it’s for either.

Answer: 
You may have stumbled onto a net that is specifically designed to allow amateurs to work on getting awards quickly by contacting others via net, such as the ARRL Worked All States (WAS) award. There's several nets that do this but perhaps the largest one is the OMISS (Old Man International Sideband Society) net. They hold several nets on several bands daily. OMISS has their own awards system also. More info at omiss.net.

Hope this helps.

73,
Sean KS4TD
If it was on the 10m band then it could have been the 10-10 club net.https://www.ten-ten.org/