Re: 264 lightning?
gene, if you can get that chamber cast you can figure out what it is. Just measure the diameter at the shoulder, the distance from the start of the case head to the shoulder and base of the neck. You can then compare to well know wildcats to figure out what you have.
There are many wildcats that have basically the same dimension but called many things.
There are only so many ways to modify the /06 case. All common varieties are well documented from the 6.5-06 to the Gibbs. The difference in case capacity is not that great so starting loads can be used.
Try to see how long that throat is. If the bullet cannot engrave in the lands before leaving the case neck, that rifle will not shoot well. You would have to set back the chamber. At that time, you could cut a more common wildcat chamber.