I have been selling the guns that I don't shoot or have no real need for as I no longer have any desire to be a collector. I have a Glock 17 Gen 1 that will be going on the chopping block in a little while and have a question about it. My example has an adjustable rear sight and I was curious to know if the Glock factory adjustable rear sight is an uncommon feature, and if so, does it make any difference in the value.