91 Mauser chambering problem

[Parashooter]

You have described the symptoms of a full-length sizer not adjusted to compensate for press flex, leaving a visible gap between die and shell holder when actually sizing a case. While this may not be the source of your problem, it's a very common error.



This condition displaces the shoulder forward as the die reduces body diameter. The result is insufficient "headspace" - the sized case's head-shoulder dimension is now greater than the space available in the chamber.

Most die makers are careful to warn about this in their instructions -

• RCBS - When setting up the full length sizer die, screw the die down until it touches the shell holder at the top of the press stroke. Then lower the shell holder and screw the die down about 1/8 to 1/4 turn. You will feel a slight thump as the leverage system cams over center. Size the case and again check it in the chamber. Size a couple more cases and check in the chamber. If these cases chamber, go ahead and size and load the rest of the cases.
• Lee - When using our full length sizing dies for rifle cartridges, the die should be turned in to touch the shell holder and then enough more that there is no daylight between the top of the shell holder and the bottom of the die during the sizing process. This is the preferred method because the act of sizing sometimes results in flex that prevents the shell holder from touching the bottom of the die. . . If you note that your Lee Die doesn't appear to push the shoulder of your case back, ensure that you are adjusting the die so that there is no daylight between the top of the shell holder and the bottom of the die during the sizing process. If you see daylight at the top of the stroke, readjust the die downward and repeat sizing until it disappears.

Many handloaders apparently miss the part about the added adjustment, stop when they merely have contact under a no-load condition, and never bother to check for contact during sizing. While this often works OK for rifles with generous chambers, it isn't good enough for those with precise workmanship and tight tolerances.