The Orca Upgrade Pack V5.3.D by Hoffman Tactical. This upgrade pack is for the Orca V5.3 3D Printed AR-15. It contains an updated lower, that fixes a possible feeding issue, and a longer stock. The last update pack, V5.3.B, contained an extended stock butt. The difference with this V5.3.D stock is that the neck and the butt have both been extended, resulting in a more streamlined appearance. The pockets for the threaded inserts have also been updated to be perpendicular to the surface of the neck, making installation easier. Note that the V5.3.D stock butt and neck are not compatible with earlier stock components. However, they are fully compatible with earlier lowers. So, if you want to print the new stock, print both the neck and the butt, and assemble them together. The V5.3 Orca lower had a design issue that made its way through testing, the magazine sitting too low. The result was that some rifles had feeding issues. The V5.3.D lower moves the mag catch up a little, and makes the slot a bit tighter. This does require a little bit more hand fitting of the slot with a file, and magazines are also somewhat harder to insert on a closed bolt, but these changes completely eliminate the feeding issue, Several other small improvements where made to the lower. The most obvious is the slots made on the bolt catch pin support lugs, these prevent cracking in undesired areas. The V5.3.D lower is fully compatible with V5.3 uppers and stocks.