There was a time when the 20's just couldn't match the 12's in performance especially if you wanted to stretch things out a bit. Those days are gone for the most part.
It really comes down to the kind of slugs you are willing to purchase to wring the maximum performance out of both the 12 and the 20. There are many manufacturers that offer a lot of variations on "High Performance" slugs for both, however if you look a little closer you will see that there are some variations that will effect performance, especially downrange. There can be a fairly large difference in the claimed velocity from one manufacturer to another, some af that will have to do with the load itself, bullet weight and barrel length for the stated velocity. If you select both 12 and 20 ga that states 1900 FPS second you are shooting one of a few that are the fastest offered today. Next will be bullet itself and the BC. Some of the old copper solids and brenneke slugs fly like a brick. Most newer designs use a all copper bullet for better downrange flight, penetration and weight retention.
If you look at the power and range they are pretty similar will the 12 having some advantage on retained energy when you get out past 100 yds. As an example a 12 is still carrying 1136 ft lbs at 200 yds, a 20 is at 877 ft lbs. The 12 at 100 yds is 1774 ft lbs, the 20 is at 1484 ft lbs
If you set both guns up with a 100 zero both will be around 1.5 high at 50 yds ,zero at 100, and 1.5 low at 125.
If you set both up with a 150 yd zero both will be around 3 high at 100, zero at 150 and 7 -8" low at 200
The wind drift is also very similar with a 10MPH crosswind the 12 will drift 3" at 100 and 13" at 200 yds, the 20 will move 3" at 100 and 15" at 200 yds
All of the above number are using the slugs that I use in my 12's and 20's. These can change big time based upon what slug you purchase so check on your own what you intend to purchase.
http://www.federalpremium.com/products/details/slug.aspx?id=994
http://www.federalpremium.com/products/details/slug.aspx?id=996
Which gun is best for you is really up to you and how you hunt. If you are a hunter that likes the idea of quick followup shots a 870 with a rifled barrel will serve you very well. If you are a stand hunter that wants to take one shot and know exactly where it is going then the savage 220 might serve you better. Both guns are plenty accurate and work great.
One advantage to the savage bolt gun is that it was built for the sole purpose of accuaracy with slugs. If there is any downside of the 870's 1100's, 1187's, Mossburg 500's is that I seen many that will not shoot the 3" "High Performance" slugs anywhere as well as they shoot the toned down 2-3/4" slugs. The Savage will shoot the 3" or the 2-3/4 both very well. I know somebody will come on and say that their 870 or 1100 shoots 1" groups all day with the 3", I got it, it does happen, I also know first hand that it doesn't always happen.
I'm sure you would enjoy either.
Good luck,
Kim
