RipOne
I'd say it mostly depends on two things. The caliber of the gun and the caliber of the shooter.
Some calibers, like pistol rounds seem to be the least accurate. That said, many are showing 1" 50yd groups with 357 and 44mag barrels.
When you get into rifle calibers, most are MOA, some slightly above and a lot well below. A lot depends on whether or not you handload.
My 45-70 Buffalo Classic could print 3 shot 100yd groups with 400gr Speer bullets, using a tang mounted peep sight. My sons' 223 regurlarly makes 3/4" groups using Winchesters white box ammo.
Mine does the same with handloads so far, but the barrels is still new.
Do a search for the caliber you're interested in and see. Some calibers have a definate prefference for a bullet type/weight.
My Savage 30-06 is almost as picky as my Handirifle is. Be more specific and we can help with even more info.