Hmmmm.  I have never heard of the mod to which you refer.  Could it be a difference in the bolt stop?  Something akin to the change in the Krag cutoff change where the bolt stop needs to be in a certain position to remove the bolt.  I have LNs from the first contract and the second contract.  However I am three months away from them to check if there is any difference in the stops.

There has been a couple of thoughts on what killed Sarco's DeRuitter.  One was a double charge of fast powder and the other was reformed Krag brass.  A bolt stop in the wrong position could be bad juju.

Let me know if you ever want to give the LN a new home.