Ulfberht rifle with Bill Alexander and Kevin Collins.

[nincomp]

Both are CIP, but evidently the actual chamber dimensions have floated around a little, even while the cartridge has been fixed. Interestingly, both .338 Lapua and .338 NM have the same OAL according to CIP guidelines, completely negating the whole intended purpose of the Norma, which was to allow a shorter action.

I can understand why Bill Alexander is wary of the .338 Norma Magnum. There are effectively two chamberings with which I am familiar.
When the .338 NM is loaded with the same bullet as the .338 Lapua Mag, the OAL of the NM can be less. When both cartridges are loaded with the popular 300 gr Sierra Matchking, in particular, the action for the .338 NM could be shorter. This was a bigger deal several years ago when there were fewer rifle actions that could accomodate the longer .338 Lapua.

The last time I looked, I did not see any common .338 bullets with a longer ogive than the 300gr Sierra Matchking used by the .338 Lapua, so the NM and the LM were evenly matched despite the OAL difference.

The "long" version of the .338 Norma Magnum, however, is a different animal. This time, it is loaded to the same OAL as the .338 Lapua Mag. The longer chamber can be used with a longer-ogive, higher BC bullet or a bullet with a greater volume for increased payload (tracer material, incendiary chemicals, or high explosives, etc). This is largely why General Dynamics chose the NM for its machine gun. The potential payload increase can be seen in the photo on the second post in this thread.