I will be taking up grouse hunting in the fall (level of seriousness depends on the performance of my pooch, but I think he'll do great) and semi-competitive "duffer" level trap shooting.  In the next year or two I would like to get a semi-auto 12 gauge, probably the Beretta Urika due to its light weight and easy handling.

My preference (stemming in large part from my affection for AR15 carbines[:)]) is for a shorter barrel.  But how short is too short?  I'd like to get the 24" barrel to keep with the light and quick theme, but don't want to sacrifice too much performance.

Any suggestions?

LOL!

But how well does it zap clays at 50 yards?  [;)]

EDIT:  Oh, and I guess I should say that the priority list goes like this:
1.  Grouse and other upland bird hunting.
2.  Trap/skeet/little orange bird hunting.
3.  Home defense (got the R6530 for that!).

get a 26"

24 inch would be a little short. 26 inch with multi-chokes takes care of about eveything.

Get two barrels if possible. For wingshooting 26-28" is preferable. For home defense, 18-20" is best. If you can only have one barrel, try for the 22-24" range. My ideal shotgun has 4 interchangeable barrels: 28" with multi chokes for wingshooting, 24" rifled barrel w/sights for sabot slugs, 18" smoothbore with sights for buckshot and regular rifled slugs, and 20" with multichoke for turkey. I don't think they make a semi-auto with that kind of versatility.

I have an M1 super-90, with a 19.5 inch rifle sight and 4shot extension for fun and a 26inch vent rib for hunting and clays, with two barrels and nine choke tubes I can wack anything a shotgun can shoot.

I think the 24 is a good all around lenghth if you only plan on one gun.I have an 18.5 and i consider that on the short side.