I am having the same problem with my early mk2 after fitting the Vortek breech seal. Underlever much harder to close and bends the barrel downward resulting with POI drop ~60mm at 16m.
Wondering about seal thickness as I measured HW (old, may be original): 4.1mm and Vortek 4.6 with a much harder compound.
Could someone explain what/where this lip is please .