I am currently working on a .405 for a friend. I first converted the barrels over and somewhat modified the buttstock so that I could shoot it and get it close before restocking it. I can tell you that with the loads we agreed on,(a 300 grain bullet at 2100 FPS), this caliber has plenty of horsepower. I didn't think it recoiled much more than a good stiff 45-70 load. I was somewhat apprehensive about building one on the .405 because I had never done one before or even thought of it as a good double rifle caliber. The man I'm doing this for wanted it to weigh between 10 and 10.5 pounds, and it will do that when I'm done. For myself, if I were building one for me to shoot, I would make it between 9 and 9.5 pounds. Good luck with your project.
What I do like about the .405 is that it shoots the same bullet weight as my 45-70 but because it is a smaller diameter, the .405 has much better sectional density and holds its speed up better than the 45-70's do. I think that with practice, the 405 could be a good 200 yard iron sighted gun, BUT, you would have to practice with it alot and get to know the sights and the gun intimately. Bob