I will comment on the barrel clamp "contraption" by first stating that it is typical of the style and build of such devices.

Secondly, and more important I call your attention to the fact that attached to the top of the adjusting wedge is a block of steel to represent the weight and size of the final front sight ramp that will be attached to the barrels. This is very important as the weight and size of such a ramp affects the regulation of the barrels greatly and if one were to regulate the barrels without the ramp attached the regulation once the ramp was soldered in place afterwards the shot placement could be anywhere.

Lastly, I will state that I do not believe all gunmakers use such a barrel clamp device, but they are useful for regulation. The only difference in building such a device from my point of view is that I use screws that have very fine thread pitch as the coarse thread pitch on the screws as pictures can be difficult to adjust to only a few thousands of an inch movement of the barrels---screws with thread pitch something like 32 threads per inch is more appropriate.

Kindest Regards;
Stephen Howell