I have a 243 catbird.
It is based on the .270 Winchester case necked down to .243 and blown out with a 35 degree shoulder.
68-70 gr. bullet ................... 4100 f.p.s.
85 gr. bullet ........................ 3800 f.p.s.
95 gr. Nosler Partition ......... 3500 f.p.s.