In a recent article in Handloader the author noted the changes in design of the Core-Lokt bullet from the past and the currently produced versions. The old design used variations in jacket thickness to controll expansion, the newer was a simple cup and core bullet. The 264 mag produces a lot of stress on a bullet, and I'd be less than comfortable with other than a controlled expansion bullet. Also I believe the case capacity of the round is most fully utilized, in any of the larger magnum rounds, by the heavier bullet weights available for that caliber. In the 264 I use the 140 grain Nosler partition. The exterior ballistic difference between it and other 264 caliber bullets of similar weight and style is quite small. At extended ranges, in most cases, the energy of the lighter bullet will be surpassed by a heavier selection due to the sectional density differences of the bullets. Eventually the greater speed of the light bullet looses out to the better retension of the heavier. I call it the pingpong ball effect. You can throw a pingpong ball very fast, it just slows down very fast also..