If it's a shotgun you are after, I'd suggest a Mossberg 500. You can buy barrels tailored for specific jobs and they are easy to change out; it takes about a minute. Pick your load based on what you are hunting, put on the apporpriate barrel, and you are good to go. Additional barrels cost a lot less than buying a new shotgun for each kind of game you hunt!
If you posted about shotguns then I'd include the Remington 870 in the version you can afford. If you can afford more a Remington 1100 or 11-87.
If you can afford more then a Beretta double either O/U or S/S.
for smaller game the shotgun is where it's at. it's great for hitting those moving targets.
Your range will top out at around 50-60 yards (maybe more if you are good and have the right chokes and loads) with "shot" (the multiple pellets), but standard slugs can go over 100 yards and still have the punch to put down a tractor-truck. Sabot slugs, which require rifled "slug barrels" can stretch a 350 grain .68 caliber slug out past 300 yards, dead on target.
I always reccomend Mossberg for a shotgun, but ti's doubly true if yoy want something light as they have aluminum receivers.
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As people have posted above, the low to mid range pump guns will do. But I much prefer something with a little more quality than a mossy 500.
For upland or mid size game you should look into a 28, 20, or 16ga side by side shotgun. They cost a pretty penny, but will hunt longer than you can and be something that your proud to pass down. Plus the light upland shotguns are balanced and weighted for long days out in the feild. It should help on fatigue.
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