I hit nothing with 3 BB shots at 20 geese at 40 yards today, and then missed 3 Black Ducks with #2s at 35 yards. Bah!
I like how many folks blame the shells all of the time, Mountain, not laughing at you, just the statement. To reply and add to what everyone has said so far will be a long post, so I will try to summarize the best that I can.
Stop guessing, you need to pattern your gun, plain and simple, no getting around this one, to truly understand what your gun is doing. Early season birds in your lap, using #4's, sure your throwing a larger pattern with smaller shot. Can't achieve the same results now using larger shot size? Less shot, longer ranges, could be your pattern is spread too thin, again patterning your gun will tell you.
Maybe your point of aim is off, smaller shot size, may compensate for it, larger shot size isn't, ever think of that?
Don't always think that a full choke is the only way to achieve that killer dense pattern, change your mindset a bit. I can achieve dense full patterns with my 20 gauge using IC choke. You do realize that steel patterns tighter than lead, right? A modified choke will throw full choke patterns, and a full will throw x-tra full patterns, usually, mind you, there are always exceptions to the rule.
Larger shot sizes usually benefit from quality after market tubes with longer parallel sections, keep that in mind. I have done plenty of patterning with my guns, and they all throw different patterns, using the same choke style/type shot size....interesting right?
Most all of my guns have screw in chokes, a few don't. I still shoot my old (35 years) Smith & Wesson auto, 30" barrel fixed full choke. Back in the day, that was what all or most waterfowler's used, long barrels and tight constriction for that wonderful stuff called lead shot. I will shoot #2 steel through it, but nothing larger, as I don't want to blow the choke out, besides, my patterning test showed that is what works best with it.
You DO NOT need to shoot the candle sticks (3 1/2"), or even 3" shells, believe me. I won't shoot anything larger than 3" shells, have I shot 3 1/2" shells, yes, I personally do not deem it necessary, most of my shooting has been done with 2 3/4" shells.
When steel was first mandated, I had to switch to it, I think it was back in 1983, where I hunted. I went through different brands, all 2 3/4", some performed well, others not so much. One of my favorite loads, believe it or not was 1oz. of shot in a 2 3/4" shell, out of that same S&W gun, I killed a lot of birds with that load, and at distances greater than 25 yards, even a few geese.
I have a gun that came with 5 factory chokes, I tried them all with various loads, they all sucked! So, aftermarket chokes were next, the improvement in pattern density and shape were obvious, and very favorable.
ALL of my guns, except for the fixed choked ones, use aftermarket chokes, the improvement in using them was justifiable, by the better patterns that I was getting.
What I'm telling you, are my experiences in shooting Ducks/Geese/Pheasant/Turkeys/Doves etc... for over 35 years, this is experience talking, backed up with data, not some internet jockey who read it somewhere. Take it for what it's worth.
I never saw the benefit of wad stripping chokes, didn't do anything "x-tra" for my patterns, so I don't use them.
I definitely have no need for the Black Cloud chokes
I settled on Trulock chokes, SK2 and IM for most of my guns, albeit I do have a Terror choke, that throws a mean pattern, it is tight, and I only use it in certain conditions.
Other folks have very good things to say about Carlson, Briley, Kicks, Colonial Arms, Indian Creek, Pure Gold (what I use for Turkey's). Ever heard of the Ceramic Teflon infused Muller chokes? most haven't, what about Sumtoy? These are a couple of the not so well know brands, that are very good indeed.
If you take anything away from this, remember, if you center the bird in your pattern, at a reasonable (killing) range, you will bring that bird down, you do your part & the gun & shell will do their part.