Well a friend (maybe we will see) gave me a box of L7A1 9mm ammo. Supposed to be 50,000 PSI subgun ammo. From the internet they say it works fine in Glocks.
I intend to chrono it and I'll let you know, presuming I survive, how fast it goes.
I'll use a Glock 17 and 19 for the test, and a face shield.