There is an alternate version which drops down more, it retails for an additional $120 or so. After going back and forth for a few days with [email protected], I chose to remove the bayo lug on mine.
It was a difficult decision, but I rely more on a light than a bayonet.

Surefire has it. It's not in their catalog or their website, which is why I had no idea it existed. I'll look through my old e-mails and see if I can locate the part number...

Here's the e-mail transaction between myself and Surefire help. The model # of the right one is included. They start at the bottom, with the most recent one on the top:

=======================================
Dear Cory,

    I asked about using an A15 adaptor for you shotgun.  It is not stable
enough to work without failing.  Changing batteries would also be a task as you
would have to remove the fore end every time you needed new set.

Best regards,
XXXXXX XXXXXXXXXX
Technical Support


-----Original Message-----
From: TREETOP . [mailto:[email protected]]
Sent: Monday, September 30, 2002 6:47 PM
To: helpyou
Subject: RE: Problem with new weaponlight...


XXXXXX-

I'm very close to just milling off the lug, but there's something I may try:
Will an A15 work in this case? It seems like it would offset the lamp enough
to the side to clear the lug even with a bayonet mounted.
Maybe you've got one there and could mock it up and let me know?

I appreciate your help in this matter.
-Cory Price.


>
>
>Dear Cory,
>
>I do not have a picture to compare the 623A01 to the 623.  The 623A01 is
>set up to clear the bayonet lug.  The clearance between the magazine tube
>and the lamp module is greater than that of a standard 623.
>
>Sincerely,
>XXXXXX XXXXXXXXXX
>Technical Support
>
>
>-----Original Message-----
>From: TREETOP . [mailto:[email protected]]
>Sent: Friday, September 27, 2002 11:32 PM
>To: helpyou
>Subject: RE: Problem with new weaponlight...
>
>
>XXXXXX-
>
>Thank you for your quick reply. I'm trying to locate a picture of the
>623A01, and I've been unable to find one. I'd like to see what the
>difference is. I can't find one in the "2002 SureFire Weaponlight Catalog"
>that I got from you guys at the 2002 SHOT Show, and I obviously didn't see
>one on your website or I would've known before I ordered mine. I'm not sure
>why there would be no mention of the 623 not working on bayo-lug equipped
>590s on the website or in the catalog, the information would've saved me my
>current headache.
>I didn't buy this directly from SureFire, I bought it from another online
>source based solely on a cheaper price. Perhaps if I would have called in
>an
>order directly I would've been told that in order to make it work for my
>application I'd need to cough up an additional $141, but that's about twice
>the amount I paid for the standard 623.
>Depending on what the 623A01 consists of, I may or may not upgrade. If it
>sinks the lamp module further into the foregrip, I may be interested. If it
>lowers the lamp module further from the magazine tube, I'll try to figure
>something else out. I'm leaning more towards milling the bayonet lug off,
>and replacing the barrel if I ever decide I want it back.
>*Yes, the light is more important to me than the ability to attach a
>bayonet
>to a shotgun.*  :)
>
>
>Please let me know the difference between the 623 and the 623A01. If you've
>got a comparison picture that would be ideal. There's always the
>possibility
>I'll move this 623 to one of my 500s, and purchase the 623A01 for this
>particular 590.
>
>Thanks for your time,
>-Cory Price.
>
>
> >
> >Dear Cory,
> >
> >      Thank you for your inquiry regarding SureFire products.  In order
>to
> >clear the bayonet on your Mossberg 590, you need to use the 623A01
>system.
> >If you purchased your 623 from us we can exchange it for a 623A01.  There
> >is a retail difference of $141.
> >
> >      Surefire is dedicated to providing world-class customer service.  
>We
> >appreciate your interest in our products and welcome any future inquiries
> >and comments.
> >
> >Sincerely,
> >XXXXXX XXXXXXXXXX
> >Technical Support
> >
> >
> >-----Original Message-----
> >From: TREETOP . [mailto:[email protected]]
> >Sent: Thursday, September 26, 2002 10:43 PM
> >To: helpyou
> >Subject: Problem with new weaponlight...
> >
> >
> >
> >Greetings.
> >
> >I've got Surefire weaponlights on 5 of my personal firearms, and I've
>never
> >previously had a problem at all that was Surefire related.
> >Today I received a light for my Mossberg 590 that I ordered recently, and
>I
> >have an issue with it that I need help finding a solution for. It's a
>model
> >623. It is clearly labeled as being meant for the 590 as well as the 500,
> >but it won't mount to my 590 because the lamp assembly would make contact
> >with the bayonet lug on the barrel ring. My first thought was milling the
> >bayonet lug off, but I don't want to resort to that since I like having
>the
> >option of fixing a bayonet. I doubt this is the first time this has
> >occured,
> >what can be done to remedy this issue?
> >It seems like a 3v lamp assembly would sit behind the lug, but even with
> >the
> >P61 lamp the 6v one is just bright enough for my needs (I've grown
> >accustomed to the 9v P91 lamps on my AR-15s). I'd like to keep the 6v
>lamp
> >but I don't know what to do here...
> >
> >Much thanks in advance for your help.
> >
> >-Cory Price, aka TREETOP, moderator, www.AR15.com.
> >
>