I would go with your middle of the road modified cylinder choke. As for ammunition it depends on your living situation. If you read the posts titled "penetration" the general consensus seems to be #1 buck shot is your best bet for a 12 *****. If you live in an apartment or the bedrooms of your family members are spread out in various locations throughout your home and you are worried about penetration of walls and such, many reccomend a realy heavy bird shot or #4 buck would work fine. There are some very large posts with lots of information on this subject, I recommend looking them up and reading those as well.
Well..as sonde said, birdshot through #4 buck in a modified would work just fine, i however would open up the constriction a bit more. I would use a improved cylinder, with the big stuff. 1 buck through 000 (Those dont treat a modified to kindly). Besides they say that 1 buck is the most effective in a twelve gauge and has a stopping percent of 87-90.
And should you chose to use rifled slugs, an improved cylinder is the best to optimize the accuracy.
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