Surefire forend for $270-ish and slap it on. Unfortunately, Surefire's forend apparently doesn't work well with the 590A1's bayonet mount/sling mount--you have to basically file that part of the shotgun off, which was a no-go for me.
Yes, there's always the options of just drilling out the existing forend and adding a piece of Magpul railing - cheap, and generally works. But, I wanted something a bit less redneck and a bit more sturdy for Project 590A1.
The Ergo railed 500/590 forend was just the ticket. Remove the factory forend/pump and this baby slides right into place, giving you three sections of mil-spec picatinny railing to slap whatever tactical accessories your heart may desire.
Disassembling a Mossberg shotgun is not particularly hard and there are an abundance of videos on YouTube to help with the job. Switching out the forend is more involved then changing out something like the stock, but it can be done in 15 minutes with minimal tools on the kitchen table.
I'm very happy with the Ergo rail--it's rock solid and does the job well.
While I don't plan on adding oodles of tactical accessories to the shotgun, I have added a Magpul AFG to help with the ergonomics and a weapons light is in the near future...and that'll be about it.
The Ergo rail is not the cheapest route for mounting a light on the Mossberg, but it is certainly one of the best. All-in, with a
$100 weaponslight like a Streamlight or InForce, or even a Surefire flashlight in a quality mount, you're still well under
the price of the dedicated Surefire forend.
And, you've got a more modular system than the dedicated forend, too - if you need to change out your light - say you're switching to an IR light when running NVGs - the picatinny rail lets you make that change quickly and painlessly. Works for me!