The Webley 400 & 700 definitely have some design flaws. One is in its hook design. These guns do tend to come off the face fairly early in their life with moderate use. Another is how the guns action wears over time, the gun tends to over gape over the years causing the the forend to dig into the bottom of the action floor plate. This is caused by excessive wear to the cocking mechanism. The mainspring pins on the side of the actions have very little thread bearing surface and these usually back out or strip out over time as well.
Overall, I love W&S BLs. None of these flaws would ever prevent me from owning one. I still own a few.
My vote for best overall BL design goes to the W.W, Greener Facile Princeps or FH series guns. These guns are ridiculously strong, petite actions, the internals are robust and hearty....the fastening system is far superior to the W&S series too. Youll rarely see these guns in the shop for action issues or being off the face.
