My old eyes don't see as good as they use to even with the implants after cataract surgery. Peep sights have their advantages and disadvantages but I liked the one on my Crosman 1322 so I decided to design one for my 747. What I ended up doing was making a plate with the aperture in in it and glued it to the existing blade sight. After getting it sighted in today I was shooting nickel size groups pretty consistently. I designed it in Freecad and 3D printed it.