Umka, that is cool - I didn't know a person could put a diopter peep on a Mosin. I already shortened the rifle I want to put a peep sight on so it needed a new front sight anyway (please nobody hate me, it was counterbored already). I filed a dovetail to install the taller front sight I made for it, as Mosins tend to shoot high, and was going to sight it in with a brass drift, hammer and file. With a modified bolt a sight like the one like your picture would be really cool - I was originally going to make an aperture slider like my Arisaka as I quite like shooting it. Just not sure yet how I'd make one like your pics, but now I'm not in a rush to cut down that front post.