At first glance that .577 round looked like a 40 mm short.
From Wiki
The
.577 Tyrannosaur or
.577 T-rex is a type of
cartridge developed by
A-Square in 1993 for
big game hunting in Africa. The .577 contains a .585-inch (14.9 mm) diameter 750-grain (49 g) Monolithic Solid Projectile which when fired moves at 2,460 ft/s (750 m/s) producing 10,180 foot-pounds force (13,800 J) of
muzzle energy.
[
10,180 Foot Pounds!
Uffda!
Don't think there will be a handgun taking that round.