IMO- as you asked Charlie-I will use any 12 side-by of the moment, if I use one of my 12 M12's- after all the waterfowling is over- I take out the 3 shot plug--Crows are all feather and NO body mass- if you can get them inside of 35-40 yards, whether to decoys or a caller, I like a mod choke or imp. mod 12, and 12 AA 1 &1/8 skeet loads- No 8 or No. 9 shot.
Last year a good gunning friend sold me at his cost- a case of those loads never fired (he gave up skeet due to failing vision- ) he bought them from his gun club some eyars ago at $4.75/box- all were No. 9 shot- and boy howdy- did my average on incoming crows and barn pigeons to up--deadly swarm- But whereas No.9 will drop a crow or pigeon, I would never use them for game birds-don't dare carry any lead loads for crippled head shots on mallards due to the steel shot laws-
If I am after some "archangels" pass shooting near silos where soaring crows are also airborne, I love my cannon 2E Smith 32" Full&Full VR-DT- then I use either an AA 8 or 9 or sometimes a No. 8 spreader in the first barrel, and a Handicap AA 7 & 1/2 shot size in the left tube-
Someday I'll have a nice 32" tight choked 10 double- then the crows won't know what hit 'em- like my sharpshooter buddy who hunts squirrels and rabbits (standing shots only, if the critter is running he gets a "pass") with a M70 Westerner in .264 Win Mag- was with him after coyotes a few Winters ago- a solo crow landed in the midst of a snow covered picked corn field we had staked out- He used a FIR and centered the crow with a handload at Mach-4 velocity- about a 125 yard shot with 5 mph crosswind (est'd) as i was his spotter with my binocs-that crow blew up like he had sat on a C-4 cupcake- Wow!!!
PS- Charlie- I still have those 12 once fired empties for you!!