Originally Posted by Kevin Thomas
Yes, but you won't know just how much. Invest in one of the gages, even one of the cheaper ones, and you'll be ahead of the curve. Need to know what you're moving here, and the only way to do that is to measure it. That's where the gages come in.
Kevin's absolutely right on this one.
The reason is, depending on how much case lube's on the fired case and the difference in diameters of the fired case and die, you can easily have a spread across two dozen cases of 3 to 6 thousandths of shoulder set back. Good case cleaning and lubing processes can get the spread down to under 3 thousandths.
When you get the case gage, use it to full length size your cases such that the ones with the highest sized case headspace reading is about 2 thousandths shorter than the average reading you get from measuring several fired cases. This insures that all your cases will chamber easily. And even the ones that had their shoulders set back the most will still be safe in your rifle.