Thank you all for your comments.

Max H. I will keep in mind the possibility of interference with/from my spectacles and go and try a sight at my local gunshop.

As for the 6x Acog Murphy, that would appear to be better mounted on a military grade .50 calibre rifle, than a light weight air rifle for close range pigeon shooting! You would certainly do maximum damage to the pigeons though, not to mention the surrounding countryside! I guess the pigeons would be well plucked after impact!

Jim