Here is the minimalist of gun cabinet organizers. Designed at 15mm for Glock and other polymer lowers with wider trigger grips, these slide-together puzzle pieces included some glue-in spacers which allow it to work down to my little Browning .22 1911 which has a trigger guard of 8mm. Take that 5mm spacer and in your printing software, turn off uniform scaling and adjust the width to whatever you want! For 1911's and long barrel guns, you may want to elevate it by mounting it to a piece of wood or simply printing a base. It fit all of my guns including the full size 1911 but it didn't hold on to much. but it really doesn't need to.
I printed 3 spacers on the bed at the same time. One at 4mm, one at 5mm and one at 6mm.