All other things being equal, there's not a significant difference between 5's & 6's in either pattern density or the amount they can destroy flesh. But if you're out there past 35 yards, particularly on going-away birds, 6's have a tough time penetrating. Go with 5's in both barrels (assuming you're talking about lead shot or something roughly as dense) if you think longer shots are likely. Close birds......6's are fine. I'd only go w/ different shot sizes if I was really sure most of my first shots were going to be pretty close. All depends on type of birds (wild/planted) & type of dog (flusher/pointer/experienced/novice). I'm a one barrel, one choke, one load type of guy. My brain can't afford to be cluttered up with that stuff when it's trying to tell me when to pull the trigger.
So I've come to the conclusion that with the exception of my Browning Sweet 16, that I shoot my over and under 20's better than anything else. After years of hunts, I have the can of cast off shells and usually grab what's available. But...for those of you who shoot 20's at pheasants; do you go with 3" mags or stick with 2 3/4? I'm not trying to get in a brand or shot size conversation. Just talking overall power here. What do you guys think?
Personal preference but for me the 3" isn't necessary to kill pheasants. I reload and 1 ounce of #5 at 1250-1300 fps does just fine.
#5 bismuth also does just fine at 1300 fps (Kent's 16 ga. factory stuff). You probably won't be able to cram 1 full oz into a 2-3/4" 20 ga. hull; maybe more like 7/8 oz. But if you get the velocity up in that 1250-1300 range, you're fine for most pheasants. So I agree. 1 oz of lead 5's at 1250-1300 is all you need. You need to put it in the right place at the right time, but if you do that, you're fine.
I meant that it's hard to find for reloading.
Ballistic Products usually has most shot sizes in stock. Used to have a manual full of data for bismuth. Don't know if they still do.
I have never been a fan of Bismuth and opted for one of the Hevishot offerings.
3" 20....... Just shoot 16 or 12.