If the case and shoulder diameter are undersize, thus 'should' fit - the only difference is the length of the body (or neck) - ie: the body length of the brass that will NOT fit, is too LONG from the base to the start of the shoulder - thus the solution is easy. If the overall length of the brass is correct, the over length necks are NOT the problem, the body length is. If the brass is too long, case length trimming is necessary. It is dangerous to shoot brass (binding at the case mouth) that is too long for the chamber.

If the problem (probable cause) is the body length, simply FL size the brass, pushing the shoulder back enough to JUST allow it to chamber.

This same problem with a different gun, but with the same too-long a body was experience by another shooter at another shooting forum I frequent. Due to the small size of his .17 Ackley Hornet case and the ease of sizing them, we suggested shaving a few thousandths off his shell holder.

With larger cases, like the standard or magnum rounds I do not suggest shaving the top of the shell holder as this weakens the shell holder's strength, thus it's capability of withdrawing the ctg. from the die. I had just such an altered shell holder that I keep to remind myself and/or to show others with similar problems. The top part of the shell holder became ripped upwards when extracting a sticky case.

I had removed too much (obviously) from the top of the shell holder.

Thus, I now always remove just a bit from the bottom of the die, (grinder or lathe) to make the cases size properly for the chamber.

The solution is simple even if the die will not push the shoulder back far enough - material must be removed from the bottom of the die to allow the case to enter further up into the die, thus pushing the shoulder back the requisite amount.

Be careful not to push the shoulder back too far, as you will be creating an excessive headspace problem with THAT brass.