Man, I go away for one week and the ability of the crowd to catch a basic problem goes up in smoke!
Flyboyjake,
Your Lee die is working correctly. If you haven't noticed, the 7 mm Rem Mag is a belted cartridge. It is designed to headspace on the belt, so the shoulder is located to be sure the case shoulder making contact with the chamber shoulder does not prevent the belt from making contact with the end of its recess in the back of the chamber. Looking at the SAAMI drawing (download
the SAAMI rifle drawings PDF file and open it in Acrobat reader, then in the upper left where the page number is, type in page 56 and hit ENTER), you will note the upper drawing on the page is the cartridge and the lower drawing is the chamber. The dimensions have unilateral tolerances in order that the given numbers represent critical limits explicitly. The critical criterion is that the cartridges always fit into and fire in the chamber. They cannot be too big for it. So the numbers given for the cartridge are maximum values followed by minus numbers that are the tolerance range. Oppositely, the chamber numbers are minimum values with plus tolerance ranges so the chamber can never be too small for cartridges that conform with the standard. The maximum cartridge and minimum chamber values are the tightest possible squeeze fit that will still work. However, manufacturers usually don't give you a dead minimum chamber and don't normally make a maximum cartridge. Usually, new cartridges are made at near minimum values.
The case belt has a minimum distance from the bottom of the case head of 0.212" (0.220"-0.008"). The chamber belt recess has a maximum distance of 0.227" from the breech face. That's a difference of 0.015". The shoulder of a new case then has to be sized so the case can slip at least 0.015" into the chamber before the shoulder of the case touches the shoulder of the chamber. That is what you are seeing in the dimensions your sizing die produces.
So, now you know why belted magnum cases are famous for not lasting through many reloads. Lot's of shoulder stretching forward and sizing back. If you adjust the headspace by turning the barrel closer to the breech, you have to move it no closer than the GO gauge allows to be sure belts on all makes of cases will all fit in your chamber. That will not be enough difference to compensate for all the shoulder gap. You could customize your chamber by shortening it still more until the tallest (from the bottom of the head) belts that you have will just fit, but be aware that any brass or ammunition that you might buy in the future that has higher belts will then not fit. The whole purpose of the GO gauge is to give you the minimum space all belts that are made to the SAAMI standard will fit into. If you try to move the shoulder of the chamber back to bring the chamber shoulder closer to your case shoulder location, you probably won't be able to fit any cases into the chamber; not without the belts jamming to prevent you from closing the bolt on them.
The next question is, can you headspace on the shoulder instead of headspacing on the belt in order to get better case life? Probably. A lot of people do it, but there is a constraint. If you headspace on the shoulder, you cease to run the cases into the sizing die far enough to narrow them back near where the belt stops on the ledge of its recess in the chamber. This is OK unless or until the case fit in the chamber gets too tight for the case width to fit into it easily. At full magnum pressures, this is not an uncommon issue. The same thing happens eventually to all rifle cases that are neck-sized only and fired at high enough pressures to gradually fatten and tighten their fit in the chamber. They just hit a point where full-length resizing has to be done at least once, and then the reloader can go back to neck sizing again until they get hard to fit again, or the belted magnum owner can go back to sizing just far enough to headspace on the shoulder. The complication is if you intend to feed the cartridges from a magazine instead of loading singly, you may then run into an issue with ease of feed in the span of fewer reloading cycles. But there is no reason not to try headspacing on the shoulder to see how it works out for you and your chamber. You just set your sizing die high in the press so it only pushes the shoulder back a couple of thousandths.
If, as can happen in some instances, that shoulder set-back widens the case too much below the shoulder, there is a special
collet case narrowing sizing tool for belted magnums that is made by Larry Willis and that narrows them all the way down to the belt. Because the belted magnums are all based on the 300 H&H, the same tool works with them all. However, it is an investment, so you want to try without it first to see if you really need it.
Or, should this change never be considered?