My 74 year old eyes just cannot properly focus on a deer and a front sight and a rear sight at the same time. At least not well enough to hit anything. As a result, I have switched to peep sights and with a light gathering (TruGlo) front sight. I recently completed a Lyman GPR (Pedersoli) Flintlock kit in 50 caliber. I tried a Mable Bullseye Rear Sight (as shown in the first photo) but the ring around the peep was way too thin to be useful for me. Playing McGyver, I then took the rear sight that came with the kit (second photo) and added a steel washer to it creating a homemade version of the Marble Bullseye (third photo) with a much more pronounced ring surrounding the opening. The opening in the center of the washer is .215 inches. Using the factory dovetail for the rear sight, the peep is approximately 11.5 to 12 inches from my eye. It works really well for me as demonstrated by the fourth photo which is a 50 yard target I shot sighting in the rifle using 70 grains of FFFG and a Lee REAL 250 grain bullet lubricated with TOW mink oil. I will finish adjusting the sights when the weather is cooler than 95 degrees and the humidity is less than 80 percent! The enlarged ring around the opening does not seem to obstruct much of my view and your eye can instantly center the front sight. It costs just a few pennies for the washer and a brush full of flat black paint. For my purpose at least, it seems to be a winner.