Good evening to you!! Standard Magpul forend will not cycle properly with a Black Aces Tactical quad rail due to clearance issues. You must use a specifically modified Magpul forend (such as the one modified by GG&G) that has been designed to work with the Black Aces quad rail for proper cycling and function.
Modification is Necessary: The stock Magpul forend is incompatible and will interfere with the Black Aces Tactical quad rail. Hope this helps. Have a good rest of your day.
🇺🇸🇺🇸 'Merica' 🇺🇸🇺🇸

It will cycle without any issues I believe.

Hi Jason, The BA Quad Rail rail is designed to work with OEM forends. All other forends will need to be fitted to the rail. For a Magpul forend, you will need to cut it and fit it to the rail. Take your time, and take little off each time, and check fitment. You can get the Magpul MOE forend to fit tight, and look like it is part of the shotgun and rail.
Stay safe & have a great day!

No, the standard Magpul Forend is generally not compatible with a quad rail system like the Black Aces (BA) Quad Rail as both components serve the same function and occupy the same physical space on the firearm. A quad rail replaces the stock forend (handguard) entirely.
However, a special, modified Magpul forearm is available from some manufacturers (like GG&G) that is specifically designed to work in conjunction with the Black Aces Tactical Quad Rail on the Mossberg Shockwave 12ga. This modified version is engineered to provide proper clearance and ensure the weapon can cycle correctly.

Hi Jason and welcome. Yes Sir, the Magpul fore-end will cycle no issue. Cheers and enjoy!