Brass Sizing issues

[17LiveFree76]

Full length resizing in a belted magnum each of three times they've been loaded with (I will assume) top-end loads will certainly result in case stretching. Case failure is the next stage, and on a belted magnum most usually will develop with case head separation just above the web.

Incipient case head separation (in other words, "hasn't happened yet, but just around the corner") MIGHT exhibit on the exterior of the case in a thin bright ring. It is BEST detected by dragging a "feeler gauge" (a wire with a small 90 degree bend at the end, sharpened) on the inside wall of the case in that area above the web. If a "snag" is felt, that case is done.

Set your die (on once-fired brass) to just kiss the shoulder. If that brass does not chamber readily, take a small turn on the die. Try again. You should be able to see the travel marks of the die (neck portion) on the exterior of the neck, to know when it approaches the shoulder of the case.

Do this with your brass dedicated to one gun, and it'll last just as long as any ol' .30-06.

Edited to add: If you are expecting top level accuracy, mixing "ages" of brass (times fired) or brands of brass is counterproductive. Each lot of brass should be kept separate, loaded separately as a lot to itself, with documentation that will verify later.

I have solved my mystery. I have never had an issue like this before loading for this rifle. I load batches of 100 rounds so I haven't loaded for it in about a year. Going through my set up, dies, lube procedure etc. I realized I had changed 1 thing new since the last time I loaded. I normally have always used a RCBS shell holder with RCBS dies. A few months ago, I purchased a new set of Redding precision shell holders for my 300wm This was the first time I had used them. I switched back to my RCBS shell holder this evening and suddenly I was able to bump the shoulder as much as I wanted. My die is bumping .002 with the die barely touching the shell holder. I guess Redding shell holders are not compatible with RCBS dies

 

[DizzyJ]

I've always bumped my shoulders .002 and this rifle has no issues shooting accurate at 1000 yds. This is the first time the shoulder is growing in length instead of bumping back and it doesn't matter how far I thread the die down it will not push the shoulder back

You might need to trim a few thou off the bottom of the die if it's bottomed out on the shell holder and not bumping the shoulder back enough.