270, I think this would be pretty close to Keith's old 334okh except he used a 333 dia. bullet... another thing unless one has a fondness for the 8mm which I don't, if I were looking at this wildcat, I would go with the std. 338 dia. bullets because there is such a wide assortment available to the handloader...there is a great deal of enjoyment in havingsome thing different...I made the .300 H H because it is not seen much now..Old Keith was making new rifles when he was 80 years old...I think it kept him young...if I had only hunted with my old 06, things would have gotten boring pretty quickly, and I doubt I would have the interest in it that I do today.... Right now I am thinking of the calibers to use this fall.....this sounds like fun, but I would go 338