Cornered Rat,
This might work for you. Contact Marble Arms. For about $100, they will shorten your barrel to any legal length you want and install a Poly-Choke. This is a variable choke, just twist it to get anything from open choke to extra full. They have two versions, one plain, one with a muzzle brake.
http://www.marblearms.com/
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Dorsai
Personal weapons are what raised mankind out of the mud, and the rifle is the queen of personal
weapons. The possession of a good rifle, as well as the skill to use it well, truly makes a man the
monarch of all he surveys.
-- Jeff Cooper, The Art of the Rifle