I designed this so that it would hold the shells firmly so that they wouldn't fall out while hunting or sporting, but you don't have to break your fingers every time you need a shell. The holder will fit any length of shell (2.75"-3.5") as long as it is a 12 gauge. I advise using a heavy brim on this part and a thin first layer to ensure that the numerous "ears" won't curl off of the printbed when printing. I have also modeled one for 20 gauge shotshells which can be found at this address: https://www.thingiverse.com/thing:2733997