old colonel,
I think they are a mistake mostly because they have no rim. I am one of those old farts that beliaves a tipup rifle of any barrel configuration "belongs" to be chambered for a rimed cartridge;also other single shots, but not quite so strict for #1&3s.Pressures are also a factor, especially in 308 and 243. My friend Walter Grass reported that in his o/u double rifles, 30-06 was the third most requested caliber( in 1970s),but still prefered a rimmed cartridge( 9.3x74 was first, 7X65R second). If a customer demanded it, he would build a combo gun in 243, but said they always caused problems.If they wanted a 308, he talked them into 30-06.They can take the pressures, but shoot loose quicker, and give more problems with extraction.
Mike
