It may be more than what you want at this point, but here's an old post of mine:
I'm at work and it's getting busy, so I'll add to this post in small pieces as I can.
First let's assume, and yes I know what that can get us \:D , that the dimensions of the chamber and sizing die are within the normal range and there are no pathological brass problems. Furthermore since I'm primarily addressing the original poster who is new to the game I'll avoid mentioning measurement tools a real beginner may not yet have on his bench.
The main idea is to size the brass just enough to chamber the way we want while not excessively moving the brass around. We'll be working with brass that has been fired in the same chamber it's headed for now. We'll be full length sizing, but barely enough.
Remove the expander ball assembly from the die. When we're doing the initial adjustments we'll be passing a single piece of brass through the sizing process a number of times. We're trying to get the body and shoulder of the case sized the correct amount and while this is getting ironed out there's no reason to size the neck down and run it over the expander ball a bunch of times.
With the proper shellholder installed in the press ram, lower the handle so the ram is in its highest position. Thread the die into the press until it touches the shellholder, and then back it out a turn.
Clean a case really well with a piece of steel wool, paying particular attention to the neck and shoulder areas. Wipe it down with alcohol and after it dries color the neck and shoulder area with a permanent marker. After the ink dries size the case.
More than likely when you examine the case you'll see the ink disturbed part of the way down the neck while the ink on the shoulder is undisturbed. We're going for getting nearly all of the neck sized without messing up the shoulder. The shoulder is going to get bumped eventually, but not too much.
Just to check, wipe the lube off the case and see if it smoothly chambers in the rifle. At this point it should.
Turn the die in 1/6 turn, re-lube and size the brass. Check out how far down the neck is getting sized. Is it close to all the way? Is the ink on the shoulder being touched by the die? Does the case still chamber without resistance?
As this process is repeated 1/6 turn at a time you'll most likely reach a point where nearly all of the case neck is sized, the die still hasn't disturbed the ink on the shoulder, but when you try to chamber the brass the bolt won't close on the sized case without significant resistance, or maybe it won't close at all. After the extracting the brass from the gun you'll see the chamber has disturbed the ink on the case shoulder.
This is the critical zone. The die has squeezed the body of the brass below the shoulder, and this has caused the length of the case from the head to the shoulder to increase. Yes, increase. Remember when you checked the shoulder ink after sizing it hadn't been disturbed by the die. What we want to do is size the case a little more, just enough to eliminate the chambering difficulty.
Clean and re-ink the case. Screw the die into the press another 1/12 turn and size the case. Has the shoulder ink been disturbed by the die?
Yes: Try the case in the chamber. If it chambers with just a little "feel" upon closing the bolt you're almost done.
No: Turn the die in another 1/12 turn and repeat.
So now you've sized and resized this piece of brass so it chambers with a small bit of resistance when you close the bolt. Sounds good, right? Well almost.
You see, a piece of brass that hasn't been through the die as many times as this one will not size down quite as much in one pass. So the die will probably need to go into the press a little bit more for perfection, say 1/24 turn. Give it that final little adjustment.
Install the expander ball assembly back in the die. Lube a different case, including the inside of the neck, and run it through the sizer. Wipe it off and try it for fit in the rifle. If the bolt closes with little or no resistance you're golden.
This procedure is one of those things that's harder to describe than it is to demonstrate. If someone who knows the ropes was there with you they could have you up and running inside five or ten minutes. Once you learn how your sizing die and rifle chamber interact with your particular lot of brass you can set up the die without having to jump through these hoops again.
mathman
