I would suggest you try Brenneke KO elcheapo slugs. I have used them for several years, with great success. I have a Mossberg 500 12, with a full length smooth bore. I have not lost a deer that I have shot and hit. But all my shots have been under 75 yards.
My second suggestion, determine your range. Look at the area you will hunt, decide how far you think your shots will be. Be realistic. If you hunt a heavy wooded area you will probably not get a 200 yard shot.
If you are hunting where you will get long range shots. Check into a rifled barrel. The range is better. The accuracy is better. Cantilever style barrels(scope mount made on the barrel) appear to be the best. Don't buy a used barrel, unless you trust the person. I have gave 3 away. All 3 were suppose to be like new(NOT) I tried several Brands of ammo, with no luck. I went back to my smoothy.
Try several (more than a couple) brands. They are most likely to shoot different from one brand to the next.
Have fun and good luck.
Keep us posted on how it works out.
Lonny