Gentlemen,

If a sized, but not loaded piece of brass has the same problem, it has nothing to do with seating depth.

bottlerocket,

You have the FL die down flush to the shell holder, with no gap. You can still turn the die down another 1/4 turn past flush, and "cam over" your press to bump the shoulder back. If the marker trick shows a slight rub on the shoulder, then they will need bumping back.

This will probably fix your problem.

BUT--

If you're running the die down to the shell holder and touching without sizing a piece of brass in it, you will have a slight gap between the bottom of the die and the shell holder when you do size a piece of brass. The extra resistance of sizing a piece of brass will take the "play" out of the press linkage, causing the ram to travel slightly less distance (we're talking a couple of thousandths here, like a sheet of paper thick). This could be just enough for your FL die to not bump the shoulder back. You can check this for yourself by shining a light at the die/shell holder all the way up with a piece of brass in it, and look from the other side for a hair thin gap between them.

You've loaded ammo for this rifle before, but I take it this is the first time you've had chambering problems? Is this the first time you've loaded fired brass, or have you been able to reload brass before that was fired in this rifle without this problem? Are you using the same die set and shell holder as before?

You may have to experiment with another brand FL die that is slightly "tighter" than the one you're using now.