Hi
Great shotgun, how long ago did you buy the barrel?
A few years ago I wanted to make a M2 field/camp shotgun were I would just have a standard 28" barrel to use at sports clay and then get a 2nd 18" barrel to use when out camping. I contacted Stoegar and they stated that was not possible as the 18" barrel only came with the m2 tactical and had the ghost ring front sights and if I had an m2 tactical with a 18" barrel couldn't buy a 28" for it and also the ghost ring rear sight on the m2 would have been a problem.
Is the 18.5" barrel you have with rifle sights for the 3+1 action like the field models I believe they do the 5+1 for the m2 tactical models
Thanks
Del