If your shell holder doesn"t securely grip the sell and firmly fit into the press during reloading, you"re bound to have headspace and sizing problems. RCBS manufactures their shell holders to the industry"s tightest tolerances, using only the finest steel.#43 Shellholder fits:223 Winchester Super Short Magnum70 Winchester Short Magnum7mm Winchester Short Magnum300 Winchester Short Magnum338 Winchester Short Magnum