The ONLY reason for a circle-reticle front sight insert, would be for bulls-eye target shooting, so that the bull can be precisely centered in the circle.
I would never try it on game, sticking to a bead-type front for the proper use of any tang or receiver peep sight - NEVER consiously try to center a front sight in the aperture !
Simply look THROUGH to aperture, AT the front sight bead/tip, and place the front sight "on target".
The rear barrel sight should be either removed or folded down, for a clean/clear sight picture through the peep.
The human eye will subconsiously auto-center itself in the aperture, allowing accurate shooting (ask any Olympian).
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