I've been a sucker for good Model 12 HD guns ever since I hunted with my first one, many moons ago near Moosonee at the southern tip of Hudson Bay. Some good stories came out of that trip.
I probably have too many HDs right now but it's so hard to part with one, especially a solid ribber.
Dave commented on the 3-inch/1-7/8 ounce lead shot load. They work OK in HDs and I've shot a lot of them in years past but IME their recoil is a bit too much in these ~ 8-3/4 pound HD guns. They were designed for H.V. 1-5/8 ounce loads and nowadays that's the max lead or non-tox shot load I'll use in a HD for long range work.
Here's another M-12 Heavy Duck, a 30-inch solid rib, straight grip/wood upgrade with somewhat higher and longer stock dimensions than standard. 1947 gun with .729" bore and 34 points of choke. Too nice to hunt with? Naaaah.