Ghost ring / peep iron sights for air rifle or 22

Minimally usable “iron sights” to keep on a picatinny rail when the normal optics / sights are removed. The ghost ring and post is accurate enough for some plinking with a .22 or air rifle and stays in place with just friction. Light enough they just stay in place. Could make a variant with through rail retention screw.  Sight picture is surprisingly usable.  

I've printed them in PETG and PETG-CF with good results. In PETG-CF might need to be scaled up (101/102%) or lightly sanded if it's too tight. Depends on your printer and filament.