What Snag and others have said. The nock taper is put on before the back taper. Sometimes the nock doesn't fit because the taper is a little long and the point taper keeps the nock from fully seating, as Macbow pointed out.
Solution is to just nip a little off the tip of the taper. This works, even if the arrow diameter is actually less than 5/16 at the start of the nock taper. The shoulder of the nock may not be flush with the shaft, but it will fit solidly.
If you cut off the entire taper and re-tapered the nock with a hand held tool, it's quite likely it didn't come out straight and probably came out too long as well (because you had to use the 11/32 guide to accommodate the increasing shaft diameter).
It's possible to regrind an accurate taper using a shim against the shaft on a taper jig on a disc sander, but it's about impossible to do it with a hand held tool. Hope you didn't cut off all the original nock tapers.