I have a primitive "peep" sight on my deer rifle (.50 cal Allen Martin Schimmel). Years ago I found a swivel base screw that was designed for a Brown Bess musket (or so it was advertised). In place of a normal bolt head, they machined a ball/base on the top of a 8x32 tang bolt. They then drilled a hole through the middle of the ball to allow a swivel screw to pass through it. Being a fan of peep sights, the wheels began to turn.
I filed each side of the ball off to leave it with the flat "lollipop" shape. I then carefully filed the underside of the base to match the shape of the countersink in the tang. After installing it, I found that when the front sight is centered in the aperture, it is also centered in the rear sight notch (although it looks like you are holding the front sight high in the rear sight). The rifle shoots to point of aim at 75 yards with this setup and I have killed ten deer with it so far.
One thing I like about this setup is that when I want to shoot this rifle in an open sight match, all I have to do is swap out the "peep" tang screw for a flat-top tang screw. The open rear sight stays in place all the time.
I shoot a high front sight and did most of the initial sight adjustments with it as LRB mentioned.
galudwig