I am a little confused, as usual. If you are loading for a 300 win and your dies aren't set up right and , say, you are bumping the shoulder back too far, that shouldn't affect head space what so ever. Belted rounds are designed to head space off of the belt. I neck size only on all of my hunting guns, so I head space off of the shoulder, so after the first firing the belt is useless to me. If the brass had been fired in that gun I can't see how it is possible that the brass could be too long. What I have seen on three different factory guns is the chambers are reamed "out of round". On two of them, the chamber was wider on the north south axis than on the east - west. So, the only way the rounds would fit was if they were rechamberd the same way that they were fired. I could make them fit if I rotated the brass until it fit. I never had a chamber cast made, but it was plain as day what the problem was when I measured fired rounds. I tried to fix the problem by FL sizing the brass, but that didn't work. The brass was bad right from the belt and I couldn't iron it out. The funny thing was that Remington didn't have a clue....after three months with the guns, they sent them back with two of their own new brass, which they had fired in the gun. "No problem found. Gun shoots fine". I called them and tried to re-explain the problem and that the brass that they sent back would only fit in the gun when rotated to a certain point. They just couldn't grasp the concept...."but.....the gun shot fine, our ammo chambered w/o any problem, we can't help you" :confused: :mad:
So, try that. Measure your once fired brass, before you run it through your press. Or try and re-chamber the brass at the range. If it chambers rotate it 90 degrees and try it again.
Now if this is a gun that you have had for a while, and the problem just mysteriously started....well....then.......a......NEVER MIND:o