Im going on a 2 day duck hunt in December. Not sure how we will be hunting yet. The guide said he will scout the day before and we will go where the ducks are. My question is what choke are you guys/gals running for waterfowl? I will be using bismuth 3" #4 shot out of my Beretta A400 excel. Any help is appreciated.

For me; kind of depends on how the ducks are behaving, and if I’m combo hunting geese simultaneously. If I have a chance at geese while hunting ducks or if the ducks are actually setting up, and landing with the decoys - Full Choke. If the ducks are flyers, and won’t set up - Modified Choke. (like Teal)
The full choke with ducks that are setting up will help you save a few decoys too.

Bismuth likes tighter chokes.

For Bismuth I would start at mod and if further shots go to IM or Full.

Put a couple in your pocket and change if needed.

You are over thinking this. For decoying birds and #4 bismuth:

Improved Cylinder if it is going to be an in your face hunt.

Modified is about perfect for ducks over decoys out to 40 yards.

Full choke if you shoot well enough to shoot the close ones in the head and neck and center up on 50 yarders. Having a shotgun with more range sounds better than it is for most. It will cause the average wing shooter to miss more of the up close candy birds that should be meat in the pot.

1) Improved Cylinder if you want to shoot them over the deeks.

2) Full Choke if you want to skybust.

3) Modified if you want to shoot them over the deeks, but maybe also do a little skybusting...

4) If you want to focus on skybusting, don't use Improved Cylinder, or you will be skyblasting, not skybusting, there is a small deference there for those taking notes...

That is a nice gun. I bet it comes with a nice set of chokes, designed specifically for that gun..

This. I’d start with improved mod. I’ve noticed my patterns with mod and anything less restricted is junk with bismuth.

Thanks for the info

Pattern your gun w shells you will shoot at 20-30-40 yards. You will be shocked, if doing it right, how many of your shots are at 20 or less…….

I have no problems with a modified choke and 3" #4's Federal Speed Shok. All about being on a target

Pattern, pattern, pattern. A lot of guys find the right load for their rifle but don’t give a thought about what a specific shell and choke does. These days I typically use 90% apex #2’s and a Full Carlson and 10% of the time a Light mod and Winchester #4 in another shotgun. I typically am on the outside shooting clean up. so my shots are usually a little further than my buddies. Those combos pattern well and it’s usually either a DRT or complete miss. I went to a shell and full combo to give me range and adjusted my shooting to it.