Would love to take my old full choked M12 out for some geese next season and due to the age and the choke I will be loading bismuth. Would the 2s work for decoying geese? I am going to be using a 1 1/8-1 3/8 ounce load depending on what the patterning board shows.

Sure it will work. I would use BB'S for longer range shooting, depending on the pattern board as you say. Look at Tom Armsbrust's Bismuth manual that is sold by Precision reloading.

I actually have the buffered loads manual from him and the bismuth is next on the list. I do have one concern in that gunsmiths have told me the tight full choke is fine with bismuth but other (non qualified) people have told me that it could damage the gun. I am leaning towards the gunsmith's opinions personally.

I think going with the gunsmith is the smart answer. Bismuth reacts well to buffer & choke. High antimony shot, particularly buckshot, can be harder than bismuth. Real hard buckshot in a real tight choke could conceivably expand the choke a little. Buffered bismuth?? I sort of doubt it! I have killed turkeys on the wing at 60 yd. +/- range with buffered #2 bismuth & I have had great luck on ducks @ over 40 yds. with buffered #5 bismuth. I haven't shot it in extra tight turkey chokes but I have shot it in full choke 10 & 12 ga. duck & goose guns with no problems.

If you will look , you can see Lead is 11.3 g/cc and hard lead is around 5% antimony
but good Bismuth ( the 6% tin type) is only 9.6 g/cc so it's soft and it won't harm your barrel !
I do Buffer my Bismuth , reason being , it keeps it together in the pattern and to do this I use
.025 constriction ! I do shoot my Mod 12's and Wingmasters with fixed chokes !
Follow the recipes to the Tee , as , buffer builds pressure ! Thumbs up for #2's buffered !

I believe the general "rule of thumb" is to go about 2 (1.5) shot sizes larger when shooting bismuth shot than what you would shoot using lead shot. So your bismuth #2 would be about equivalent to a lead #4 pellet.

Pellet density is not an indication of pellet hardness. Steel shot is less dense than lead or bismuth shot and is much harder.

"Pellet density is not an indication of pellet hardness."
True, I didn't mean to imply that it was. Bismuth is less dense than lead & I have heard the "two shot size larger" thing before. Yea, I think most folks would agree going larger is a good practice. The experience of others may vary but I have found that with buffered bismuth, 5's & 4's work well as do 2's for geese. I would go to BB's for the longer ranges on geese.

Geometric, my remark about density and hardness was not directed at you. The post below your 2nd post by Ravenanme discusses density and softness.

Yes if I need be corrected ? Bismuth is heavier than Steel Shot but lighter than Lead so
We find that Bismuth hits the target harder than Steel because it carries more energy !
I shoot a lot of Bismuth and my finding is , going up 2 sizes in steel shot , I see about
the same effects ! I do like Bismuth in 4's for ducks and 2 's for geese as I shoot these
through a .025 constriction as well as .036 / .038 in my Mod 12's and Wingmasters !
The good part , if there is one is , with Longshot and conventional Lead Wads , it is
easy to load a super Waterfowl load !
Remember , pattern density is your friend , take all you can get !

noweil,
No problem. Since I was talking about the density & hardness of shot, I thought there might be some confusion about what I said. Apparently, there was not & is not & all is fine. I am not the world's leading expert on bismuth or anything but without doing the math, bismuth is about 87% as dense as lead & about 25% denser than steel. It is a little harder than lead and good bismuth shot is more resistant to deformation & in good loads, can perform as good or better than lead. They perform pretty much the same in the field, in my experience. Note that there are more bismuth pellets in an ounce of a given shot size than lead.

Thank you very much everyone! I will be placing an order for bismuth to start patterning and finding a load that works for my gun soon.

Remember , Bismuth doesn't need a lot of velocity , 1300/1350 fps is plenty !
The Lymans 5th has a few loads to start off with but I like Longshot /800X loads
best with .025 to .038 chokes in my 12 ga's !

"Remember, Bismuth doesn't need a lot of velocity----"
Very true but few people seem to understand the relationship of shotgun velocity & effective range. The only ways to increase down range lethality I know of is to increase velocity, pellet mass &/or pattern density. Look at ballistic tables such as those compiled by Ed Lowery, formerly of Winchester. You will see shot from a shotgun sheds velocity like a rubber duck sheds water. It is most beneficial with steel as steel needs the most help. 5 yds. increase for a load effective at 40 yds. is 12.5% increase in range which can mean a lot if ducks are hanging on the edge of your kill zone. The denser & heavier a pellet is the better it retains velocity/energy & the easier it is to compensate.

I certainly agree with you , I'm just stating with Bismuth #2's , payload is more
important at longer distances ! The larger pellets require less velocity as they deliver
more energy farther out . I do like Fast Steel shot loads , some Lightning loads with
7/8 oz of #3's do a Dandy job on Big Ducks !

My only comment on Bismuth (and I've been shooting it since 1996 or so) is that all there are good bismuth brands and not-so-good Bismuth brands.

Bismuth needs about 5% tin alloyed in it to prevent fracturing. Most of the bismuth I have shot is bismuth company bismuth bought in bulk for reloading. I did buy some Winchester 10 ga., 1 7/8 oz. #2's I got a deal on years ago. I still have a bunch of it. It's great stuff & will also clobber turkeys on the wing. The only time it performed below par was on an extremely raw day hunting geese in N. Dakota. The wind was blowing a full gale & it was clear & frigid. We were getting small groups of both snows & Canadas but they weren't committing to the decoys well & shooting was on the edge of effective range. There were 8 or ten in our group & everybody was shooting steel except me & one other guy were shooting bismuth. One small group of dark geese (aka: Canada geese) came right to me. I shot the lead bird & when the feathers parted on his breast, I swung on another bird. When I looked back for my goose, he wasn't there! You could actually see feathers move & hear steel shot hit the birds but none fell! After the shoot, a guy came walking up to us from a different group with a dark goose & said, "I believe this is your bird." He saw the whole thing & marked where it went down.

Final score: 1 dark goose
2 snow geese

bismuth shot : 3 geese
steel shot "0"

I have mashed decoying specks and snows with Boss #3 bismuth. I would think that #2's would be fine.