What kind of accuracy could I get, if this is possible ?

Absolutely..... The Mossberg 590 is a police duty/ Military duty combat shotgun. It has a smooth bore no choke barrell which means you can shoot anything out of it. Only 2 3/4 inch or 3 inch 12 gauge cartridges or course.... The 590 can shoot slugs, trap loads, buckshot, skeet loads, pepperspray loads and even sabots. I wouldnt recommend sabots as they perform better in a rifled barrel..... But overall the beauty of the 590 is it can digest anything.... Accuracy? Well I certainly wouldnt want to hunt deer with it. The shorter barrel isnt conducive for deer. I can hit deer size targets at 40 yards with mine (using 2 3/4 inch remington slugs) but thats about all the reach I think you can consistently get with an 20 inch smooth bore barrel...For hunting you want at least a 24 inch barrell ..... The 590 is more of a close range combat shotgun..... Like for knocking on doors in downtown Iraq..... The Mossberg 590 is the finest combat shotgun money can buy..... If you want one and arent sure just get it! You will not be disappointed -- They are fun to shoot!... See the below links....

YES, Yes, yes.* You will get the best accuracy if you use them in an improved cylinder choke according to the manufacturers.* Maximum effective range is 100 Yards.*

I think that to shoot slugs from a shotgun you need a rifled barrel, not sure my self.