Six rounds were given to me, some with 450 headstamp some without, they measure to be 45 COLT, but the stamped rounds have a larger rim dia
.516. and a greater OAL 1.7".
My guess is they are early 45 colt ,possibly English with the 450 designation.
The doner obtained these and other rounds with a early or antique Colt single action revolver, and generously gave me some spares.
The colt has no caliber markings, corrosion to on side where it has been laying for a long time.