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.
#8 Shellholder fits:
45 Auto Rim
WEIGHT: 0.1 lbs
MANUFACTURERS NAME: RCBS
MANUFACTURER PART NO: RCBS09208