The reasons the .243 with say 70 or 75 gr HPs, or .25 with say 75 to 87 gr HPs, was good for roos was the fragile projectile needs to stay in a chest of a roo and not exit to damage the skin on the far side. Fragile SPs as well.

Brain shots of course damage neither hide nor meat. At closer range and if the rifle was accurate enough.

.22/250s and .220 Swifts were also popular of course. And effective, But IMO and others, lack some of the power needed for consistency, a reason a .243 was preferable.

I wonder what is used today, and how many .223s?

I do think a .25/303 in a nice cutdown SMLE would make a nice vintage ex-mil rifle. And useful for medium game ferals and smaller deer species. The ten shot mag is also useful.