I have an Austrian made sidelock o/u, made in the 1930s, very similar to this Merkel, that locks up even today, tight as a rat trap, and in .270 Winchester caliber too, a very intense cartridge not generally considered suitable for a double rifle. I consider the Purdey underbolting with the German Kirsten bolting, such as this, to be one of the most excellent bolting systems ever designed, among the strongest ever designed. Though this bolting system was used on some German sxs rifles too, as well as these types of o/u rifles, I don't consider it worthy, as it makes for way too wide an action, ugly.