I'm also running the same Model 930 with "Stand-Odd/Breacher" barrel so I'll be following this thread for more info as I'm looking to do the same 2 shell extention in the near future as well s installing a rail assembly.
But for right now I'm looking at an ammo issue. I recently purchase Winchester AA "Low Recoil/Low Noise" Target Loads. It wasn't until I got home that I realized that on the bottom of the box it states, "USE in break open & pump shotguns only. Do not use in semi-automatic shotguns as load may not function the firearm's action."
Now without the receipt in hand and maybe even if I had the receipt, they wouldn't exchange the ammo. Upon asking around other's that know more about shotguns than I, about this ammo, everyone seemed to agree that it should work just fine because of the barrel being as short as it is. Now what the length of the barrel has to do with this ammo working, IDK but that's why I'm bring this to you guys that actually run Mossberg 930's with a 18.5" barrel. Will this ammo work? If not, what ammo would you suggest that has a controllable recoil for quicker follow-up?