Hey. Long time reader, first time poster. So I recently got my hands on a Mossberg 590. I of course had to order and install the Magpul forend. I installed using the anti-rotational tab for the designated for the 590. After install, the slide was difficult to rack and it would hang up quite bad in the rearward position. After disassembly and reassembly multiple times thinking I assembled wrong, this problem continued. So, I reinstalled the factory tri-rail forend and low-and-behold, smooth action all the way. So I was like, F-it, I reinstalled the Magpul forend only this time using the anti-rotational tab designated for the 590A1. Well, now I have smooth racking all around and very happy with the look and feel of the Magpul. My question is this, has anyone else experienced this? I hope this helps others as well. If you install the Magpul forend on a 590 with the 590 anti rotational-tab and racking the slide action is rough, choppy and hangs up, use the anti rotational-tab designated for the 590A1 and you will be GTG. EDIT: Upon calling Mossberg with my serial number, apparently the 590 I purchased was a special build of sorts. Its a 590 (plastic trigger guard, plastic safety) however it was sent out without heat shield, heavy barrel and ghost ring sights. It is also drilled and tapped. So, with that said, if the 590 anti-rotational tab makes your pump difficult to rack or it hangs up on rearward position, your 590 may have been shipped with a heavy barrel and will require use of the 590A1 anti-rotantional tab. Hope this helps someone.