Pause your printer just before the hex nut cavities are covered, insert 1/4-20 nuts, and continue printing. (This was at the end of layer 44 of 47 on my print)
Screw a threaded rod approximately 4 inches into the end of the pistol shelf, then a jam nut. This jam nut will lock the rod in place at the desired height.
Screw on a second jam nut about 1/2 an inch down the threaded rod. Screw on the gun yoke with integrated nut on top of the threaded rod. Use the jam nut to secure the yoke in place in the proper orientation.
The final height can be adjusted at any time depending on the size of your firearm and in what manner you want to level it on the shelf.
Simply loosen the jam nuts and rotate the entire assembly to the desired height and re-tighten.
Affix the whole assembly on a tripod to complete the pistol shelf.
Made on a Printrbot Simple Metal in HIPS using 0.2mm layer height.
PLEASE NOTE: This device is only to help steady your aim. It will NOT hold the firearm for you, and will certainly NOT ABSORB RECOIL. YOU are still responsible for controlling the firearm at all times.