How to force Ma gnus to download specific msgs en-masse

[Harry Putnam]

Setup: Debian (jesse)
Running very recent ma-gnus 

Can anyone tell me how to force gnus to download specific msgs in
large quantitly (meaning several thousand)

I used to use the agent very heavily for some yrs but for last several
yrs since gmane holds msgs so long I faded away from that practice.

Now forgotten just about all I ever new... plus some of it has changes
possibly. 

I need a quick and dirty way since this will be a seldom done thing to
download specific authors from specific groups.

Selecting that part en-masse is not a problem... I know how to do
that.  But had the notion I could put the download (toggle) mark on
them (%) on them and they would get downloaded.... 

Can anyone explain in as few steps as necessary how I might do this?

Imagine, I open a group.... select 10 (though it will be many more)
and somehow force gnus to download them...