I want to add a reflex red dot sight to my moderated .410” for my boys to use as a rifle for pooping balloons etc. It is just a fun way of making it a little more accessible for them at limited cost. I will eventually put the reflex sight onto some as yet unbought break barrel air rifle once they are strong enough to cock one.  Any thoughts on most efficient way to attach a picatinny type mount? Annoyingly the moderator is 39.5mm in diameter and so just slightly too large for the over barre