It's refreshing to say the least to not have to deal with a what program do you use on RTF, but, shotgun related to a Remington 870 opinion. OK here is my opinion on the Remington 870 12 gauge. My background with this particular shotgun. As former police officer and a patrol Sgt. for a few years the standard shotgun was a Remington 870 12 gauge 18 inch bbl with a 2 and 3/4 chamber. We shot clay birds for practice with number 8 lead for gaining confidence and of course loaded with 00 for duty work. Occasionaly we would use 00 or 0 buckshot for combat practice too. I had several women under my command and they had no issues with shooting the 870. It can be broken down with ease for cleaning etc. Short bbl did produce some muzzle blast but the low base #8's helped alleviate any flinching problems.
Moving on to the hunting issues. I purchased my first 870 Wingmaster Modified choke 12 gauge in 1968 new for I think $85? I shot Trap, (tight modified) several deer with a slug bbl and who knows how many ducks, grouse, woodcock, geese, doves barn pigeons and flyers at field trials. The slide is white with wear. Still own it and still shoot it. Later I bought a slightly used 870 with a IC bbl. Again shot so many flyers at field trials and training can't count them. It is in my truck now and used it just last week for ducks hunting over decoys #4 steel IC and shot doves earlier in the season #8's. Sitting next to it in a case is also my Browning Magnus 12 gauge all pretty etc and sometimes is next to my 390 Silver Mallard or my 12 gauge Citori. I bought the IC bbl on e-bay for about 75 bucks and use it also on phesants . I find myself using my Remington 870's more then my "pretty guns" oh yeah I am a member of a gun club too.. Now there is some fellows at the gun club who called themselves the "old Geezers" they have killed locally last count 157 geese 49 ducks between the six of them. The best shot I saw was a bonified 70 yards shot using a 10 gauge by the holder of several state Wisconsin skeet championships. MOSTLY however thier shots over decoys are 25 to 30 yards or less. In fact one of the guys has a very fine QAA retriever we three own and have trained, leaves the dog in the truck sometimes because the retrieves are too short. His choice not mine I always take my dogs. So a 2 and 3/4 steel shot Nos two, one or even BBs highbase will do the trick, in my opinion on geese and certainly except for severe pass shooting will get you all the birds you can shoot, if you can hit them. OK, now lets bring up the hitting them, buy a case of 12 gauge loads, go to the local trap, sporting clays or use a hand held thrower and practice with the case of no. 8's. I buy my cases for about $67. bucks.
My advice buy number 1 and never look back as you can check around down the road for a extra bbl. Stocks can be adjusted, might not look pretty but can be adjusted.