“I wonder what the pistol was? A drum magazine is not that common.”
You can get a Glock 9mm drum easily. A lot of people use them on pistol caliber rifles like the SU2000.
I just came across this:
https://www.youtube.com/watch?v=Zw-o3p4ZMtE
The guy is using extended mags, not a drum, but look at what a Glock will do if it’s “suitably modified.” I know you can possess something like this in Arizona if you have a Federal License.